Got to the bottom of most of the issue now. After losing my rag with 3 offshored idiots who clearly do not understand how UK clearing houses work (or the fact they exist), or how their own systems work. Tosspots.
It is a sad state of affairs that after 90mins of them stonewalling me, insisting it was a fault with the retailer's till (remember, Santander could see the transaction, but we went in this endless line of because the card wasn't blocked, and there was still credit, it must have been the shop), I had to be very blunt, honest, and sadly rude, before they would put me through to somebody in the UK who could fine out why it failed.
All of Santander Credit Card processing system went down for about 50mins, so was declining everything.
Now why the hell they couldn't tell their offshored call centre that is beyond me, as it meant I spent 90mins on the phone, listening to a pack of lies/BS, and told such stupid things (more than once) of trying to make the purchase again tomorrow.
rather retarded useless breakwits, employing India's most stupid of people.
I think I've got to the bottom of the $505.16 (declined transaction), but their is a potential issue with the times, so just awaiting to hear back from the retailer.
BTW, I support the card processing system for a major credit card company, so have a pretty good overview of how the system works
