Hi again Martin, most of the discussion on this thread has been about PAYG. As far as I know PowerUp is now closed to new customers so is this a problem with a new card? Have you been on PowerUp successfully before?
I am a customer like you and cannot sort anything out with your account. You need to talk to SP on the helpline. I am also a PowerUp customer so I am interested when thinks go wrong. You can report it to the community on the dedicated PowerUp section, this section is for PAYG problems.
My electricity needs to be topped up next week so I will see if I have the same problems. My experience with PowerUp is that it sometimes does not work correctly for a few days, but then seems to refresh and solve its problems. Your best couse is to wait until after the weekend and try to make the payment again. If it continues to reject (have you been issued with a new debit card recently?) I think you need to talk directly with SP on 0800 027 0072.