Paid contractor agreed amount but wants more? What to do?

[Peter Fokas]

Hired a contractor to some improvements to rec room in basement for 2500. Gave him deposit of 1000 to start. He kept asking for weekly payments even though we agreed to pay balance when project finished. We had some issues with him so felt better to end this working relationship. We still paid him the full amount of 2500 as agreed and told him he did not have to finish the job. Now he comes back saying he wants another 2700 for work he did that was outside the scope of original contract. Any recommendations on how to handle this?