The past tense of renege is reneged.

I don't know why you would renege on the deal.

Reverse, Backslide and Unfaithful are synonyms for the term Renege. To renege also means to break a promise or to go back on one's word, to backslide.

Renege is another word for revoke. It means to back out on a promise or contract. A good sentence would be, he thought he could renege the contract that he already signed.

The correct spelling is renege (to go back on one's word).