Need to resolve a billing error

I need assistance with getting a bill resolved. I pay my Xfinity bill via a corporate account with my apartment complex. When the account was set up and when I moved into the complex the Xfinity technician that serviced my complex was out of the country for weeks and told me that if I needed internet sooner that I should go to Xfinity and establish service, on my own and he would transfer the account and return the equipment when he returned. I did that in July and at the end of Aug the agent came to my apartment set up the equipment tied to the apartment and took the Xfinity equipment that I picked up from the store and said that he would turn it in and transfer the account to the corporate account. Now I am getting debt collections calls and I have reached out the to the Xfinity representative and now he is not answering my calls or text messages.