Just to fast track things for ease: two wrongs don’t make a right!
When they took your deposit…you had them - a contract had been entered into. Offer, consideration and acceptance had taken place! (Just put that in to jog
@Bigsidavies memory!)
When they wriggled on the “offer” post contract, you still had them under the original contract (as it had been accepted.) That’s the first wrong!
However, when you agreed to a deposit return, all bets are off. That’s the second wrong! Contract has been mutually negated, even though it doesn’t “feel” mutual. There’s no law governing feelings!
A change of mind or a snotagram email doesn’t change that fact unless some numpty salesman puts a foot wrong.
A sale now will be a new contract with a refreshed offer (aka refreshed price!)
Sorry to be the bearer of bad news…! As a matter of interest, Marshalls were bought out from family ownership by the private equity brigade. Worse, the family didn’t even let their CEO know that they were in talks with the PE crowd. So, long story short, Marshall’s have plenty of sharp pencil types to rinse you! Collect your £500 and walk away.