Poor Service and customer support

SuperSonic is claiming I have an outstanding balance on an account that I already settled. I paid the settlement amount they sent me and provided proof of payment (POP). However, they are now claiming there's an outstanding balance for the following month.

Furthermore, instead of addressing my concerns and responding to my questions, they have referred my case to VVM for collection. VVM has been harassing me with daily phone calls that they hang up on whenever I ask them to respond to the emails I've been sending since March.