Can't cancel account or return equipment

I closed my business and have been trying to close my internet and phone account for a month now.  I signed the requested documents via docusign and was told to return equipment to UPS store.  I went to UPS store and they will not take the equipment.  Meanwhile comcast business will answer the phone and tell me they are transferring me to someone who will help, but I just get put on endless hold.  And of course they just keep sending invoices for internet and phone service that I have cancelled.  Tired of the run around.  How can i return the equipment if UPS won't take it, and how can I stop the billing from Comcast for services I have cancelled?