i believed u may have already sought help from the police and
they maybe telling you to seek legal redress and file a civil suit
esp when there is absence of proofs...the "harassment messages" may
not be sufficient evidence of harassment....
this may fully fall under the jurisdiction of the law of
property....which will look into points of law regarding
landlord-tenant lease agreement.....
in UK law, tenants are usually given the benefit of
doubt....
please make police report if u haven't by the way...