Sorry to hear of the issue.
It is a common theme with some dating sites (and other sites in general) in that they lock you in.
A contract can be completed online but from what you say, you simply left the site and did not complete the transaction. They have to prove there is a contract with yourself - until they do this, there is no contract in place and you should refuse any demands to pay.
You can tell them you will speak to Trading Standards Scotland - my view is you do this in any event given the underhand tactics of the site. You can reach Trading Standards here: https://www.tsscot.co.uk
If they did escalate, they may ask a debt collection company to write to you - which is all they can do as debt collection companies have no powers. You can just reply to refuse payment.
If they sued, it would also be a small claims case - no lawyer would be required for this. It is a very simple process and the claimant has to prove a) there is a binding contract in place and b) you are in breach of contract and c) they have incurred a loss.
It should be over quickly if they did pursue you in a small claims case - my view is you challenge it and continue to refuse to pay.