Unfortunately you have already ticked that you agree: Price
3.1 Prices on the website are the prices charged in store on that day. As prices may change on a daily basis, and the website is updated overnight, prices are therefore a guide only. There may be variations by the time We are due to Deliver, or You are due to Collect, Your order. When You shop online You will pay the same price (excluding Our online only promotions) that You would pay if You came to Our Store to do Your shopping on the day of delivery.
But phone the call centre anyway, they may refund the difference! It's a freephone number, so you can't lose by trying