I'll start with the usual "I know this should be in the legal group
but..."

A company took an order through their web site and sent a confirmation
e-mail with prices for each line item and the total to be debited from
my credit card. Does that constitute a contract?

When the goods arrived they have charged a higher price for some items
and charged more to my card.

What offence has ben committed? Something under the sale of goods act?
I believe in retail premises it is an offence to charge a higher than
marked price once an item has been rung into the till, unless the
higher price is first pointed out to the customer.

TIA

Andrew