How long does it take to reverse a disputed transaction

I tried to buy medication at a pharmacy at the Netcare Pretoria East Hospital on 3 August 2018. After two failed FNB card swipes we had to withdraw money and pay by cash as the cashier indicated that there was a communication problem between the bank (FNB) and the merchant.

Only one swipe was registered and reversed (as per my InContact), however the second one did not even show on my transaction history (or pending items); but my bank account was R631.72 less (the transaction amount).

I called FNB on 4 August 2018 and I received the dispute form which I returned the same day. The email address provided returned a message that the inbox was full. Again after phoning FNB, I was told to also send the form to FNB Premier. On the 9th of August 2018, I had to write a followup email. After a few frustrating phone calls and being promised that there will be an investigation , there is still no resolution to this, and I am still R631 out of pocket. Is this the kind of service that the so called Premier Clients should get or any FNB client for that matter?