Charged for returned iPad

I returned an iPad in March. I have spent 14 hours over the past 8 months trying to get the charges removed from my bill. Every time I’m told they can see they received the return, it might be taken off my bill for a month, then it is charged again. I‘ve hear “I’m submitting a ticket” so many times and now they are charging me for the full amount!  I‘ve been with Verizon for over 10 years and spent in excess of $60,000 with this company. Does anyone have any idea how to truly escalate this issue to get it resolved?