MTN CONTRACTS ARE RUN LIKE A ****

Mtn Contracts is a nightmare, my contract ended in January apparently i had to call them to cancel! In March i paid R300 , and cancelled , they said i will get 1G and 25minutes for the last time in April and after the 20th then my contract will be cancelled ! Now my account has been suspended and i Owe R375 i don’t know how did they count that for 25minutes and 1GB i am livid!! there was also a link saying i must pay 145 i don’t know what to do , When i click on it the amount changes to 375!