Deal with contractor or supervisor?

I'm dealing with a contractor who is not performing per our contract. He is slower than promised with deliverables, his work is frequently subpar, and his communication is slow to non-existent. My suspicion is that he and his team have more work than they can handle. Earlier this month, work had to be re-done twice, which meant that a project that should have taken less than a week took two and a half. I've been trying to work with him directly to resolve issues, but after that incident, I called his supervisor. I got a response to from her two business days later, in the form of a call from the contractor, saying that his supervisor asked him to call me. She herself has never directly responded to me. What would you do at this point? Would you try again to resolve it with the contractor? Would you insist on speaking with the supervisor? FWIW, the contract is up in November, and is unlikely to be renewed by us.