I have the same problem. I cancelled my membership over a year ago, they continue to deduct the money from my account but they have handed me over to attorneys in which you cant even get through to these attorneys. I was handed over within a month of sending my notice of cancellation.
I tried to call the Planet Fitness call center and they told me nonsense about how the debit needs to continue until my contract ends and I must settle the lawyer fees. I have never experienced such bad service honestly.