FNB Connect data depletion and account placed on minus

I have an FNB connect sim card for which I purchase airtime and convert to data. I am really frustrated at the fact that when I run out of data, my account is put on minus instead of disconnecting me for insufficient data. This results in my airtime being deducted when I recharge. I purchased R100 airtime two days ago but couldn't purchase R99 1gb data as my airtime was insufficient. I am not going to recharge again as advised by the FNB connect consultant just so I can purchase 1gb. This is why i left my previous service provider and refuse to accept such again.

The last time i received a data bundle depletion notification was when I had 512mb on the 21st of October 2018 and nothing after that. I hereby request you to reverse the airtime transaction of R100 and disconnect this sim card ASAP!

Thank you