Yellobucks gone due to app errors

MTN sent me a text that my yellobucks will expire. Trying to cash it in for electricity purchases became a mission with the app or ussd code always returning an error. This is now past the deadline and my yellowbucks seems to be lost. Why it should lapse if it is a perk coming with the subscription is also unfathomable. Lousy service. I feel done in and ****med. Get your act together.