Disappointing service from Nedbank Limited

I am at my wits end with Nedbank. I purchased, and paid for, an online voucher from Nedbank on 5 March 2021 and 3 weeks later, after countless calls, emails and hours wasted they are still not able to provide me with a voucher which works. The service received is very disappointing. I have absolutely no idea how to resolve this matter, as nobody seems to care.