Pathetic security system and customer service

Someone sent me funds vai cardless service, I tried to withdraw the funds but their system told me that the transaction has failed and when I tried for the 2nd time the system told that the voucher has been used already....

Called and went to the branch and they told me that the money was withdrawn, by who I do not as I provided all the proof (slips,time frames in the slips) but still they insisted, my sister is leaving the bank and I hope you guys loose more customers as your service is bad!!!