Yes, 3 working days is normal and a week at most should be long enough to clear any payment method that you are likely to use (except using the post). Two weeks is far too long. You should consider stopping using the card and disputing any interest or penalties that get added for "late" payments. If disputing anything like this, it's best to put the details in writing.
If they've not penalised you for "late" payments, it might be worth asking which payment method they would be able to clear in less than a week. My guess is that the payments reach them after a few days and then it takes them a long time to process them.