Shocking Customer Service

I have been in contact with the customer service department for over a month with no luck. Our cash back rewards are being used as I can think that there is another card linked to our profile. The cash back rewards that were loaded to our card on 23 Jan 2019 and 23 March 2019, was used without myself or my wife even using this. Upon querying this, the only response I get, is that the card is being used in PTA? We stay in Cape Town no for the past 7 years. This back and forth emails has been going for over a month now, and I still dont know what the issue is.............