Will Never use this App again to send money. How dare you inconvenience people like this!!!!

How am I supposed to trust this app again to send funds. I sent my sister money from my app to her number and then the ATM says the voucher has already been used and some funny message saying the money may have been delayed!!!!! This is really bad and inconveniencing now I call the internet banking department and all I'm given is a Ref num and that they will investigate and I should get communication within 2/3 working days. For an app that is supposed to be instant it's now going to trial, I'm now waiting for something I sent via your app and I can't get a proper answer on what happened to the 2K I sent, are you serious???