Just Letting Failing To Control Their Tenant

In Jan 2015 my older brother moved to Germany and left his property in the hands of Just Letting. Nick Packham (Operations Manager) delegated the management of this property to Danny. In July 2015 Danny got a tenant to occupy this residence on a four month lease until the end October 2015. In these 4 months, this tenant has only paid rent for the first month and has defaulted for the rest of the lease. I was meant to move into this residence on the 31st Oct/1st Nov since the lease ended on the 31st October. Danny who was supposed to facilitate this process decided to disappear the whole weekend of the 30/31st. The tenant is now refusing to vacate the residence because he claims Danny promised him that he will extend the lease for another month, this while Danny had full knowledge of the fact that I (the younger brother) will be moving in and managing this property as he has failed to do what he was hired to. It has been almost a week now and Just Letting has failed in sorting out this matter. When I call Danny he promises to get back to me and never does. <br> <br> Please assist with this matter ASAP as I feel that this unacceptable.