I tried to call you back today, but was told that you had left the office.
Tried to leave you a voice mail message, but no one in the office knew how to  transfer my call into voice mail.
They were good about answering your phone,  however!
I will call you tomorrow morning before my first meeting at 8:30.
If I miss  you, I will ask my assistant to interrupt me when you call back.
I will be  in meetings with operations people from London and Sydney tomorrow, but can  easily step out to talk with you.

Returning your call
I tried to call you back today, but was told that you had left the office.
Tried to leave you a voice mail message, but no one in the office knew how to transfer my call into voice mail.
They were good about answering your phone, however!
I will call you tomorrow morning before my first meeting at <NUMBER>:<NUMBER>.
If I miss you, I will ask my assistant to interrupt me when you call back.
I will be in meetings with operations people from London and Sydney tomorrow, but can easily step out to talk with you.
assistant interrupt left mail good answering people london sydney phone tomorrow morning easily step meetings office tried leave transfer voice