Charged for data out of bundle

I have visited two MTN stores, phoned 808 twice and 555 once as well and yet I have still not been able to address my issue. I bought and loaded 1GB worth of data,bought at PnP, onto my phone and received an sms to indicate that the data was successfully loaded. I viewed my data remaining and this to indicated that the data had been loaded. Yet, I have received a bill clearly indicating that I have been charged for out of bundle data usage. The operator (808) also confirmed that she could not detect any data loaded on my account. When i asked how we can resolve this I was informed that I cannot be helped if I do not have my slip from PnP indicating I bought data as well as the sms I received to confirm that the data was successfully loaded. It has been more than 2 months since loading the data so no, I do not have the sms or the slip anymore. My bank statement indicating the single purchase of data for R169 is also not sufficient as the operator has indicated that this does not prove that i have purchased data. I have been overcharged and lost money and Have been told to hold for longer than 15min at a time because the operator needs to step away from her desk. NOT ACCEPTABLE!!