Operating systems are poor don't show our payments

Please guys advise me i need to open a case against this MTN cell phone company i want through a lot with them, first time They given me a wrong contract of data sim that was around February since now no solution now this december they switched off my line they claim that i don't pay them and honestly i may then very well i never miss my payment

Please help me to find the right information to open the case couse they just taking my money after that they canceled my line