MTN sign me up for a contract and i never signed for that amount.

I have a Data sim card with MTN, on the 24th Desember 2021 i were i theyre store in Vanderbijlpark. i wanted to do an Upgrade. so the ladie said someone tried to do ***** on my account i need to phone SAFPS to get a letter that it is me that want to apply for this upgrade. so i got the number, On the 10th of Jan 2022 i went back to MTN with my letter. Then they told me, they need to re apply for more Credit, i said tho the laddy but this is the same amount why do they need to re apply. i got an account today that my Contract is all off a sudden now month to month and i need to pay R278.26. I can not do an Upgrade for R199 But MTN can Decide for themself that my new contract is all off a sunnen more and know i can afford it. i want to know were did i signed a contract for R278.26 and for a month to Month Contract. I Rather cancel my Contract with MTN and Go to another service provider.