2GB Data Line @R198pm allowed to go up to R5000 !

My mom has a 2GB MTN broadband WiFi Deal @R138 per month . Her laptop crashed and we bought a windows 10 disk and installed a couple of updates . Monitoring the usage under the wifi settings we were in line with the 2GB. We got an sms on 9/12/2015 saying that the 2GB had depleted and out of bundle rates would apply. We planned to phone the auto page accounts department to arrange a top up bundle but before we could do this we got an sms stating that the line had been suspended as the account was at R4800 !Its now R5000! Upon investigation at the Autopage Store in Bayside by a very well \prepped"consultant who told us ... its how it works... you used it so you must pay .My Mom is a pensioner and qualifies for the R138 per month based on her disposable income "