Billing Concern

Good afternoon,
I no longer use Xfinity services because I moved out of my last apartment complex mid-July. Prior to that the complex took over all oversight of our internet services - billing went through them and we all had to get any existing equipment replaced to match the service they were setting up for us.
When this happened I had a credit in my account. When I moved I called to discuss getting the credit in my account refunded since I would no longer need it. The person that I spoke to said they would initiate the refund. A month later I spoke with someone else regarding the refund because I had not received it and that person also said it would be initiated.
In early November I received a letter from Xfinity stating that my refund would be issued - despite the letter saying that would happen 30 days from service being discontinued which I had been told happened in July.
This week I received another letter from Xfinity claiming that the equipment - that the apartment complex oversees - has not been returned and now I'm being billed for it. I do not have the equipment, the apartment complex does. I would like to speak to someone about next steps as I don't understand why I'm being charged for equipment that I do not have 5 months after I was told that service was discontinued