Watch out for these type of cashback deals, you may find that they are provided by the retailer and not the service provider. If the retailer stops trading then the cashback deal could be worthless. No good going to the service provider, if that is the type of deal, the provider will tell that the retailer set the deal up, not them.
Could be wrong of course, but these type of deals were on a consumer website recently, so as to make people aware.
Regarding where to post questions: Problems in Helproom: Purchases in ConsumerWatch. Remember though, the PCA forums are more for computer and computer related articles, than for mobile phones.