Just block them if you can.
It is a bit rude, but so is ringing your personal number after hours.
There is no need to tell them you're blocking them.
I have several clients who can ring me any time.
Anyone who rings that isn't on that select list, I don't even answer.
workplace.stackexchange.com/users/40669/Kilisi
Apart from blocking him, I would also try to find out how he got my private number.
If a colleague gave it to him, make sure this never happens again.
If it's listed somewhere on the website, it should be deleted.
Maybe the customer doesn't even know it's your private number.
workplace.stackexchange.com/users/86011/BigMadAndy
Instead of blocking them - let the answering machine take a message.
They soon get the idea that it is not worth calling you after hours.
workplace.stackexchange.com/users/27019/Ed Heal
If you are in a position where a customer would contact you directly your employer presumes that you have the professional experience and demeanor to directly interact with them.
After all your interactions with that customer are a reflection of the company and have a direct impact on the customer relationship.
Even if the customer insists on calling you on your personal phone outside of business hours you must show the same level of professionalism and demeanor.
But, that doesn't mean that you have to automatically accept the intrusion into your personal life.
Blocking the number should be an absolute last resort and you shouldn't do it without having a discussion with the customer and your immediate supervisor.
Jumping to the last resort of blocking the number is extremely unprofessional regardless of the of the customers' actions.
Your first step should be to inform the customer that they are calling your personal phone and that it's outside of normal business hours.
Unless you are directly responsible for supporting mission critical operations simply instruct them to call your work number and leave a voicemail; obviously let them know that you'll follow up during business hours.
If these calls continue or if they refuse to follow your instructions then you should escalate the issue to your immediate superior and work with them to resolve the issue and manage customer expectations.
workplace.stackexchange.com/users/4808/Steve
Give them your business number, tell them that it's your new number and your old number will no longer work.
Then block them from your personal number.
One could see it as slightly dishonest, but I think it's acceptable in this situation, as you're telling a white lie to protect your relationship with your client.
workplace.stackexchange.com/users/25572/Doctor Jones
Something to think about is: Does the customer think your company is solving their problem or you personally?
It seems possible that higher-ups in your organization will think that this is you forming a business relationship with the customer outside of your company with the possibility that you will take this customer with you when you leave.
I would suggest discussing this with your management and, if necessary, prompting them to tell you not to have contact with the customer outside of official channels.
When the customer calls, you calmly and politely blame it on your boss and keep doing that until they get the message.
workplace.stackexchange.com/users/74047/user1683793
I have a customer who somehow got my personal number instead of my work phone line. Since this individual has my number they believe that the office hours no longer apply to them. This person has been contacting me late (after 8pm) expecting me to pickup the phone, and will often call repetitively.   How do I tell the customer that it is not acceptable to contact me outside of the office, especially late at night?
How to handle a customer who has my personal number
workplace.stackexchange.com
<professionalism><communication><phone><customer-service>
workplace.stackexchange.com/questions/121171
workplace.stackexchange.com/users/80699/Suit Boy Apps
You should inform the customer that they should call your work number and leave a message. You could even block them from calling you on that number. Discuss the issue with your management. There are a range of options available to you, but your first step should probably be to inform that customer that this is your personal number and ask them to call your work number during work hours. If this fails, you may then wish to discuss the matter with your manager. Failing this options, there is always the choice of not answering the phone to them outside of work hours or even blocking them.
Your first step should probably be to inform the customer that this is your personal number and that they should call your work number during business hours. You may wish to consider simply blocking them. If you don't want to block them, simply don't answer the phone and let your voicemail record their message. You may want to discuss this with your manager so that this can be handled in a professional manner.