I am having an issue with the app store.

I am having an issue with the app store,in fact it is getting me down!. I was offered a free upgrade for my Tomtom app but when I tried to download apple asked that I put in my credit card details, why for a free update I do not know! and when I tried three times using my three different cards they were all refused !!!!!. all my cards are current and in good order. I also tried to download a couple of free apps with the same result.I am at my wits end with this.