BIGGEST ****MERS!!!!

I was offered a contract 2 months ago for a 499 offer. Accepted and i was told that i will be billed pro rata first and then going forward will be the normal 499. Tell me why i received an sms from them that i will be paying 719.11 i cal their customer service and i am told that its because of my subscriptions that i know nothing of and that my spend limit is on 3k and i have already spent 200 of it. hOW SO WHEN I DONT EVEN USE THE MTN SIM CARD. Someone please explain this to me!!!! Mtn if i get billed any cent more than what i agreed to i will reverse the payment and you guys will never get a single cent from me. So resolve this before the next debit run!!!!