If the contract is overdue, then why appeal when paying the calculation?

Question

Law in IT

The initial data is as follows. There is a contract, an advance payment of 50%, a calculation of 50%, a period of x days. Advance received, work completed. They did not meet the deadlines, but the customer does not make a tragedy out of this.
There is a question about the closure of works and the final payment. Usually we do without acts of completed work, so somehow we did not insist on signing them until now. And the customer says - wait, we will pay a little later, but you also handed over the project to us with a delay.
Question. How best to act if they are dynamized with payment. I believe that send them acts of work performed and a pre-trial claim. Or maybe it's a premature step. What do you generally recommend doing?

Answer 1

Acts still need to be signed. Otherwise, you continue to delay. Jobs seem to be rejected. If your responsibility under the contracts is two-sided and the same, then sign the act with the date of actual implementation. So explain to them that otherwise your responsibility will increase without an act. They will pay with the same delay. No one will go to court, as the penalties will be the same.