BILLED FOR CELL SPOTS FROM YEARS AGO

in march 2023 i changed my personal T-Mobile account to a business account. A few months later i received a charge on my credit card for 891.22. After some digging seemed like this was coming from the old personal account. I called support on 3 different occasions over a 2 month time span to rectify the problem. Each time i was told no worries we will take care of this for you. But you will need to wait until management contacts you via email which should be in 7-10 days. I was never contacted. On the 3rd call i stated that since T-Mobile still has not contacted me that i would have to dispute the charge with the credit card company. I did this and now T-Mobile has turned the account over for collections. The bill is for cell spot devices from years ago that T-Mobile states have not been returned. I do not have proof of return being years ago. Of course these devices even if i had them would be obsolete and would not work with todays cell phone technology. Also every time i called and explained i was told no worries we can get this taken care of. I have been with T-Mobile for almost 20 years and never have had problems until now. This would have never got to this point if T-Mobile would have just got back with me like they said they would. I am very disappointed in T-Mobile and would like a satisfactory resolution.