Advice on renewal with estate agents

Hi,
Last October, I let my property out to a couple with small children. An estate agent found the tenants for me on a let only and rent collection basis for a fee of 8% of the annual rent. I also signed a 5% renewal fee with them.
The tenants have been paying the rent on time - however, their small kids have been damaging the property. I have given several warning to the tenants with mixed results (and made the estate agents aware that I had done this).
I am now in a position that I have not found new tenants (and I don't want to risk a void period) so the plan is to let the current tenancy to lapse into a periodic one and see if they improve

I contacted the estate agents and made them aware of my decision. They have encouraged me to renew the tenancy agreement (on a fee of 5% of the annual rent). Surprisingly the estate agents have also stated that if I was to let the tenancy lapse into a periodic one then they will still charge me 5% of the monthly rent. As I am not technically renewing the tenancy, am I legally obliged to pay the estate agents 5%
If not, how do I go about legally telling them that I no longer want them to collect the rent and take 5% of the rent and and that I will manage everything from now onwards

Thanks,
Abbas