How do I prevent my code to be used in future builds of a project which source code is supposed to be deleted by contract?

Hi,

I found myself in a pretty toxic situation.

By contract, I can use an Asset Server to temporarily store the commissioned project.

Yet, since I paid for several assets I bought, the client agreed to delete all source code from everywhere, and not use or recover it in any way. By written and signed contract.

Now, the client began behaving in a way I really don't like, the contract is over, and even if I verbally agreed to support the project for some time, I'd like to stop working for this person.

I've also been offered to localise the project, but don't want to do it anymore. I'd rather stop eating for a week.

The client seems to be very confident to do the localisation without my consent, deliberately forgetting about the contract. Thus, using my source code. Since I don't want to get involved in suing him, are there any methods to prevent other people to keep working on the last version of a project I could leave?

Bugs, self corruption, timed events, builds not working from a certain version on, every idea is welcome. I simply want to enforce what agreed by contract, so anything that may hinder or slow down, or overly complicate attempts to break that point are welcome.

I know, it's a weird request.

Thank you.