Rogue management company issues

[Spugster111]

I rent out a property in a converted house for which the lease is managed by a third party company. No problems for many years until a couple of builders bought flats in the same building. These owners are now using the internal/external areas as storage for both of their building companies (heavy machinery/building eased/petrol tools stored indoors). The management company sends out a letter every four months or so to say they will clear the communal areas on a certain dates. The rogue builders put the stuff in the back of the van for that day and then unload it back into the property the next day. I’m losing tenants because of it and I’ve contacted the management company to ask them why they won’t just sent out a letter saying that spot checks will be carried out and items removed. This would solve the problem once and for all. The management company won’t respond to this request, I am assuming because these clearances are an income generator for them, so they don’t actually want to solve the problem. I/my tenants have approached the builder flat owners, but one of them threatens violence and we’ve had to get the police involved twice. Any advice on how I can get to grips with this problem/hold the lease management company to account? Thanks.