closed my planet fitness account 13 December 2019 and I keep getting letters of demand

I closed my account / membership with planet fitness on 13th December 2019,they keep send me letters of demand , my refer number is PF*** FROM PLANET FITNESS dated 13 December 2019

why must I pay for an account that I closed off in 2019? please hello Peter can you help me and stop this letters of demand Kind regards

,please see below Landau Debt collections Our Ref: LC488102 Your Ref: PF-*** Dear Sir / Madam, RE: Candice Palmer We refer to the above and confirm that we act on behalf of Planet Fitness (“our client”), Our client has instructed us to demand from you the amount of R2672.90 in respect your outstanding account which despite demand you have failed, and/or refused and/or neglected to pay. To avoid legal action being taken urgently make payment of R2672.90 including legal fees to date into our trust account, details of which are listed below: