Checkout was £15 higher

So managed to do a last second bid on an item this evening with my max bid at £70 and postage stated to be £6.95 bringing my max total to just shy of £77. This was fine for me and happy to pay. Lucky me i won the auction but when i got to the pay screen the costs were different. £3.38 item protection charge or something like that but all of a sudden my bid had become £83.33 and postage increased to £8.05. Seller accepted the cancellation request but does anyone know why the cost jumped to £91 all together instead of the £77 i was expecting to pay?