Cell c service poor service provider

I regret opening g an account with Cell C they force clients to continue with their.contracts . Thou my. contract was paid up 2yesrs after being with them for 5 years gave written notice that I will not extend my contract yet they kept billing me . So quick to apologize for their inconvenience yet nothing get sorted . I can't recommend them to anyone. This is what happens if you don't renew your contract they will blacklist you be very carefull. I am trying to resolve the matter for 3 weeks and they just pass the bucket to an external law firm the NIMBLE GROUP Yet NIMBLE group blames Cell C for not responding to the matter. PLEASE HELP.