Equipment Scam 2021

I have returned my equipment in person & called customer service to pay my closed account in full. 2 weeks & 20 calls later there has NOT been any account updates and there is a collection on my credit report showing I have an outstanding balance. I am outraged and at a lost. I don't know what else to do, no one in customer service knows what to do & I keep getting transferred to other dept's and nobody knows what's going on! Some claim to still see a partial balance, others say it's for returned equipment that hasn't been updated in the system and the rest doesn't see a balance at all & says I need to contact there collection agency to have account updates & removed from my credit report. This needs to be resolved ASAP! SERVICE AT COX COMMUNICATIONS HAS GONE DOWN HILL! I'm going with CenturyLink!!!