Labour will find out soon enough. The bank will contact them. Which I think is fecking outrageous. Especially if u want to torture so-called Labour a little. Or even a lot.
After a few months Labour will write to you. Ignore 'em or write your explanatory letter then.
If u ignore them they'll send you an email later on with an ultimatum date to pay by or lose your membership. If u ignore that they'll send you another email.
Stopping the begging emails is a totally different kettle of fish. Responding by saying "Starmer is a Zionist" or "Support Julian Assange, you wanker" to each email seems to reduce the quantity you receive.
Alternatively "somebody, somewhere, thinks you're a giant turd" is likely to work as well. Or just an emoji showing a giant turd might do it. Choose your colour with care. Violet might seem like fun but brown or black (after Guinness) seems to work best. A middle finger emoji might do it. Though it's a rather timid approach. And certainly not as much fun.
Make sure you enjoy yourself, that's the main thing.
Waiting u til you write the perfect email that shows them the error of their ways is likely to take time. Time during which they are still taking money out of your account.
Just get it done.
Welcome to the decent people.
Think twice before you rush to join any crap like that again...