Did you agree cancellation rights?
Is this an online course?
Is there pressure on places for those?
The short answer is that you are locked into a contract. There is no way around it. You signed a contract that did give you cancellation rights but you did not use them in time.
Leaving without paying would be a breach.
The question is what is their loss. Certainly they could not claim the full sum due under the contract . They do have a claim for the sum of their loss which will be far less than the sum due under the contract. Probably no more than lost profits.
Also, they are under a duty to mitigate their loss by seeking a replacement. If this is an online course then that is a double-edged sword because they can't argue that they kept the place open for you but equally in a course with no pressure on places you cannot argue that they can just replace you.
The reality is that it's quite unlikely that they would bother to sue you for the money but nobody can stamp out the possibility that they could. You could always offer a lesser sum in full and final settlements.
Can I clarify anything for you?
Well, there is an really. Ultimately you are liable. You can't force them not to pursue that. All you can do is hope that they do not for the reasons above.
You could offer a lesser sum in full and final settlement but I wouldn't do that until it becomes clear whether they intend to sue.
There are no risk free options.
you should understand that you are taking a risk either way.
If you are intent then tell them you want to cancel and cancel the debit.
If they sue then offer a less sum.