Estate Agents commission

Letting Agents

A letting agent introduced a tenant who remained in my property for 5 years. last year the agent did not bother to renew his AST. I wrote to them asking them to transfer the deposit to me and that I will have it protected and I will ask the tenant to transfer the rent to my account not via the agent as it the case now, and sign a new contract with my tenant. The agent replied saying that the AST state that they are entitled to the commission on renewal. Surely there is a limit to the number of years I can pay them commission. Can you please advise.