Planet fitness has taken legal action against me

Planetfitness has taken legal actions against for an account that I had paid up to close it. In the email that I sent to their customer service was that I want to close the account, how much do I need to pay. They told me 2300 immediately, I then sent an email telling them I will have money in three weeks. No one responded. Within 2 weeks I had the money n I paid them. Sent the proof of payment to them. After that they have never deducted anything from my account but today I am contacted by a lawyers demanding that I pay 5k.

I need help to sort this thing out.