I seem to recal reading somewhere that if you load your card in advance to pay for something over and above your credit limit that your statutory rights are disadvantaged in some way..
If your limit was 5k and you prepaid £7k on the card to make a 12k purchase then your (S75?) rights are based on 5k not 12k..
I did try to google this but am travelling and on my mobile so failed to find the details..