Horrible service and rude staff

I purchased an iphone back in 2022 and finished paying it including buyout which they debited from my moms account, now theyre sending me links of buyout saying i didn’t pay it, when i say i am tired of **** of a company i mean it, how does one move from such abuse? Every month its them saying i didn’t pay for my other subscriptions when i do all the time and on time, i have been a loyal customer since 2020 but they treat me like a *****.