BILLED WITH WRONG DATA MTN

I got a sim only contract from MTN early last year ,on my mtn MTNchoice 5g , it was a promotion I was getting 20gb ,10 at night ,10 anytime data plus 2gb free for a year ,now suddenly this year in February the decide to give me 5g ,when call I'm taken from pillar to post, they are requesting a copy of my contract, I'm like u have it on the system ,they said I must request it at the store I signed my contract ,I contacted the store ,they said it will take two days ,now it's been two weeks waiting for their feedback ,my question is if I signed a wrong contract how can I be billed with the wrong data bundles for a 1year and if my contract is correct why is MTN not informing that I'm getting wrong data and when I contact them the person sent me someone's contract which put people's confidential information at risk