I know for a fact the card isn't near / over its limit - I also tried 2 different cards?!?
I contacted Google using the link in the adwords system but haven't received a reply (been around 48 hours now).
Has anyone had this problem before and is there something I could be doing wrong?
I contacted Google using the link in the adwords system but haven't received a reply (been around 48 hours now).
When you say this you could mean either that you used the 'Contact Us' link on each page of your account, or that you used the form available in the AdWords Help Center. Of the two, the first is to be preferred by far - as it is much more direct.
As an aside, if you used the second method, but did not give information sufficient to identify your account, this could easily slow the response time.
In any case, I hope that things are already rolling for you by the time you see this.
AWA