Double payment took from my account

I madr an inline purchase via my debit card on 31/8/3018. I received a sms that money went out of account and I went into my banking app to see if money was not in reserve and according to the balance available it was taken off. Today on 5/9/2018 the samr amount went off and my balance is R0... I still had R358 in my bank account? When I asked at the branch why they said the merchant took a double payment which I had proof that they didn't take it off... Capitec just said that they will soeed up process to find out why but it is not their problem... This is now the 2nd time this happens...my clients that order from me products monies is not gone...there was anoyher payment made to my account and now I cannoy get the money becaise capitec took a double paymeny of R1037... I emailed the letter from merchant to them but to no avail.... I am disgusted with their non chalant I do not care way of handling their clients... M