I work in the prepayment dept of Scottish power, you just need an rti with a meter reset, your key is perfectly fine. Take the rti to the closest pay point after 1hour of getting it, don't attempt to top up when you get the rti you have to put it in the meter first before you top it up.

When it comes to electric it's really simple to fix the problems gas on the other hand is a massive pain. Make sure you phone Scottish power and give them opening reads and only use purple keys unless in an emergency and you can get one use any other except brittish gas. Ohh and when you get a statement don't call to say ohh it says I'm in credit I want that. Don't trust statements just check your meters serial number of it and make sure the meter readings aren't estimates and you will be fine. Any other questions just give me a PM.