Can anything be done if Agent has given wrong advice for the past 3 years?

Hi all, I need some help here and any advice will be much appreciated! My agent has given me the wrong advice in the past 3 years+ that it’s against the law to charge a tenant rent arrears fees (Whereas the Government’s How to Rent Booklet clearly stated rent arrears can be charged with 3% fees).

As such, the tenant has paid late monthly for the past 3 years without any consequences and eventually the tenant has stopped paying with rent arrears total over 3,000 now. I’ve no choice but to serve Section 21.

When I asked the Agent why they did not act according to the Law, I was told that it’s not their practice. Basically, the Agent denied everything and told me if I’m not happy with their service I can leave the agent.

Somehow don’t think my Agent has acted the right way here? As if they’ve charged tenant rent arrears fees in the first place then it could have prevented my tenant from late paying and now they have stopped paying rent.

Anyone with experience or legal professionals can you advise here? It will be much appreciated.

Thanks,
Kin