Npower in Stoke-on-Trent

Account number: 159205053. Trying to communicate with this Npower is an ordeal. They convinced me to have a pre-payment electricity meter and then failed to send me a key. I tried to telephone but was kept hanging on for 24 minutes. I still don't have a key and the credit added at the time of the installation is running out. I tried to email using the online service and the reply I received was that my inquiry would be dealt with in 7-10 days. What am I to do? It seems my only option is to telephone again and wait another half-hour for a service they should have provided without a call. This is corporate negligence at its worst!