I paid too much for a motorbike
The courts do not like to "interfere with a bargain". The price you paid was all part of the conditions of the contract you made when you bought the motorcycle, and you are bound by that contract.
Sellers must display the full price of any goods for sale, including VAT. But if the seller made a mistake in the displayed price, then you cannot insist on being sold the bike at that price.
Some credit card companies offer protection against finding the same product cheaper elsewhere within a certain period of time and it may be worth contacting your credit card company to see if this is part of your agreement.
You may also have rights if the purchase was subject to an advertising campaign such as "find this product cheaper elsewhere and we’ll refund the difference..." but this depends on the circumstances, and you’ll need to gather documentary evidence in support of this.