Bad Service

So I took out a new data sim card contract in June 2021 my monthly sub is R145 10GB anytime day and 10GB night, pro rata went of 15th of July R183.76 returned on the 17th of July went off again on the 5th of August, my out of data spent is set to zero on both my contacts, received an email and sms saying my account is in arears with R709.99, when I called to query this it was said that it was charged as over spent or as they call it out of bundle rate, when I explained and said but this cant be as my out of bundle rate is set to 0 I was told to download the cell c app me still trying to explain that regardless of not having the app I did the whole *147# thing and set my accounts to 0 balance the lady says its because you don't have the app so setting your out of bundle spent dose not work using the ussd code? I even went back to check to make sure it was set to 0 balance, my internet connection literally cuts off when the 10GB anytime day data paid for is finished and there's no connection, so how am I paying extra if I have not been using any extra, call center assistance is bad as connections always cut and I'm asked to call back having to explain everything to a next person again, I am not paying for services not used.