As Wendi and Matt have indicated, break is probably the most common word to use when describing an unkept promise.
If you wanted an alternative, though, you might consider renege : Macmillan defines this verb as: to decide not to do something that you promised to do American Heritage uses the definition: to fail to carry out a promise or commitment Here are a few examples of the word being used in contemporary news stories: The stakeholders, who were in a one-day stakeholders workshop, said if the government and district assembly do not take up construction of roads in the area particularly commercial roads as a priority, they would renege in fulfilling their task obligation to the state.
It’s all about investing in jobs — and by the way, if that company decided to renege on its promises, it would have to return a portion of the state money.
They paid it with the promise that the subsidies would help them recoup that money.
Now Pence wants to renege on that deal.
It isn’t fair, and it shouldn’t happen.
It's pronounced /rɪˈnɛɡ/ or
/rɪˈnɪɡ/
in American English, with a ‘short’ vowel in the stressed syllable; in British English it appears to be pronounced with a ‘long’ vowel, /rɪˈneɪg/ or /rɪˈniːɡ/.
(Pronunciation information courtesy of StoneyB).
ell.stackexchange.com/users/113/J.R.
I believe the expression you're looking for is "broke his word / broke his promise".
In keeping with your example sentence: First he promised me something but later on he refused; he broke his word.
or First he promised me something but later on he refused; he broke his promise to me.
ell.stackexchange.com/users/289/WendiKidd
When you say that one has "stood by their word", you've implied that they've fulfilled a specific obligation or promise they made by virtue of their character.
However, to say that one "stands by their word" it means that, in general, they can be relied upon to fulfill promises when they're made.
Others have addressed the negation of the first case, that is that one "breaks their word" or "breaks promises".
However, if one cannot be relied upon and makes promises that they may or may not fulfill, you can say that they "waffle" or "vacillate", or that they're "wafflers".
These words are commonly used to describe politicians who make hollow promises to win the favor of supporters.
A "waffler" may or may not fulfill promises they've made.
Their making such a promise doesn't indicate any incremental degree of faith that they will follow up with action.
ell.stackexchange.com/users/523/AdamO
The most common expression in my experience is to "keep" (meaning to stand by one's word) or "break" a promise (meaning the opposite), like so: I like Dave.
Dave always keeps his promises
Joe promised to finish the document by 5pm, but he broke his promise
I never break my promises
ell.stackexchange.com/users/307/Matt
In addition to some of the other answers, there are some idiomatic ways of saying this: If the speaker warned in advance that they would not be able to complete the deal, they are said to have withdrawn it or taken it back "
I know
I promised I'd help you move house on Sunday, but I'm going to have to take that back, sorry."
Today the government withdrew their promise to deliver a surplus.
However if there was no warning given, or if the person giving the promise had no reasonable excuse, you can say:
She promised me X, but then she went back on it
We made a deal
but then he welshed on it.
Note that the origin of this is unknown - it is not a known racial slur (against Welsh people) as "Indian giver" is against American First Nation people.
He fell through on his promise Fell through can also be applied the arrangements that have failed themselves, "the contract fell through".
Specifically with contractual or legal promises you can use default : Our buyer in the UK defaulted on our contract.
Mike defaulted on his credit card.
ell.stackexchange.com/users/454/jsj
I want a word or an expression which means  not standing by  or  sticking with one's promise , in the context of this expression:   First he promised me something but later he refused it; he should try to stand by his word.
What is the opposite of saying "Standing by one's word/promise"?
ell.stackexchange.com
<word-usage>
ell.stackexchange.com/questions/1386
ell.stackexchange.com/users/466/Dude
"Breaking your word" (or promise) is the most commonly used phrase. "Renege" is also used. The most common way of expressing this is 'break'. 'Renege' and 'withdraw' are possible alternatives.
Break' is the most common way of expressing this. Renege' and 'withdraw' are alternatives.