UNABLE TO LOAD AIRTIME BOUGHT FROM A SHOP ON 2 DIFF MTN NUMBERS

I wanted some urgent assistance from my service provider regarding a message that pops up when trying to load airtime. Message reads as follows "It seems that the service is temporarily unavailable due to unforeseen circumstances, please try again after 15 minutes. Apolgies for any inconvenience." This was from Saturday 20/07/2024, I tried on my brothers phone and the result has been the same. I have tried calling MTN on 135 from phone and you go through all these prompts without getting through to an agent or get any assistance, I tried the whatsapp and there was no luck at all as you get a robot responding...I eventually called MTN at Cresta mall a lady gave me *** number that I called and unfortunately go no assistance again. Where can I get assistance with this voucher or should I take it where I bought it?