T-mobile charging me after cancellation

T-mobile has been charging me for months maybe even years. On a plan that I no longer even have. They've be charging me 30$ for tablets that were offered to me on a special plan. I feel very disappointed because I've been with T-Mobile for over 10 years  and they tell me they can't do anything about it that they're sorry it's my fault. They tried to give me 60$ 🤦🏻‍♂️🤦🏻‍♂️🤦🏻‍♂️ I will be taking this dispute to a lawyer and to court.