Slow and bad service

I would like to know, why if i buy data or airtime on my mtn app it takes 24hous to load and this has been happining alot. I buy there because of the specials. When i phone the call center they say its a network issue. If i buy from my fnb app its loaded instantly but don't get the specials you have and pay more.

Honestly this is very bad service and issues if you need data/airtime in a hurry.