top up contract, has unexplained charges

i recently continued a top up contract, to receive airtime every month, which my mom can use. when the contract was renewed, it noticed strange charges[wasp or content charges]. i went into the eastgate branch to find out what it was, spoke to someone on the call center, who could not cancel these services. i sent a few emails to the client services, but the response is always delayed, and not helpful. from what was explained, these are charges by some third party, that when you open a message you get charged. sounds *******. mtn claims claims that these are not their charges, but are charging me on a top up account. question is, why would mtn charge me if it's not one of their services? mtn will not reverse these charges.my charges for the month should be around r180.00, bit i was debited about r515.00 the last month,and this month i received a bill for about r900.00. i have had a contract with mtn for some time now, and it seems that the service gets worse as the years go by