MTN South Africa Wrong billing

On the 3rd and 4th of November 2021 i have upgraded my contract with MTN store in polokwane ( mall of the north) for my 2 simcards and I signed 2 contracts, one was for R199 and the other one was for R299 which makes it the total of R499 monthly, now when the bill comes the invoice is too high, i then called MTN customer service to enquire about my invoice i was then told to go back to the store where I opened my contract to get help, i then went to MTN where I signed my contract and the query was opened with this reference number: REQ*** and i have been making a follow up but nothing is happening and its now 2 months and the bill is recurring, they close my lines because im owing and i can not pay for something that i did not sign for. In a nut shell they can not help me