Planet fitness handing my account to lawyers

I had a two year contract with Planet fitness, and I knew that I had to cancel my contract a month before the expiration date, so I did that and I sent an email to there customers service and they rep**** to me with a say saying that the query was closed, I even called the customer care service to confirm if my membership was cancelled, and they told me that it was, but recently I have received an sms informing me that my case has been given to the lawyers because I am not paying, but I am not sure what I have to pay for as I have already cancelled my membership with them 4 months ago, I sent an email to their lawyers telling them my story and even attaching the emails from planet fitness customer care (because I still have the emails with the conversations and names of the people who I talked to), and the lawyers promised to get beck to me in 48 hour and they didn't, and I sent a follow up email asking the progress of my query, but again they promised to get back to me in 48 hrs, and still nothing, but I keep getting sms's saying I need to get in contact with there lawyers to arrange payment of my account, I feel like now they are trying to make me pay for closing or not renewing my contact with them, which is unfair.