If you are on the more modern plans, such as Simple Choice or T-Mobile One plan, mobile hotspot is included in the plan at no extra cost, unless you've added extra add-ons.
You should be able to remove plans through myT-Mobile. Log in, then go under the plan tab, and select the specific line that you'd like to modify. There is a button in magenta colour that says Manage Data & Add-Ons. If you're unable to, then you should talk to a T-Mobile rep at a store or on the phone. 611 on your T-Mobile phone.
Manage your T-Mobile account