Nedbank app unhelpful and aggravating

For the second time in less than 3 months I bought electricity and did not receive the voucher number yet my bank account has been debited with the amount. Last time message was received more than 12 hours later. This time it has been 24 hours yet message has still not been received! Buying electricity is a necessity not a luxury one can just ignore for a day or two of doing without. I buy it when I am almost out so cannot afford the bank's delays, it's unacceptable. I can't buy more for the same thing to happen yet again. Problems need to be resolved immediately.