Dixons need to supply you the deal they advertised, even if it was an error.
Not true im afraid. often people think this is the case – you see something advertised and the retailer HAS to sell it to them, is indeed nonsense as they don’t have to sell you anything.
it is called an invitation to treat and not a contractual obligation.
to the OP, get a refund and start again, maybe push for compensation for having to use a laundrette but I suspect they wont play ball