Unethical behaviour

The letting agents do not practice ethical standards. I gave adequate notice to vacate the property and a reference of someone who might want to rent. Weeks later they contacted the reference and when he didn't want to rent they tried to say I did not give adequate notice. Nearly 2 years after my lease ended they contacted me about a missing fibre box saying it was missing at the end of my lease. They try their luck to get money from you.