gutter problem

Maintenance

hi
I own a mid terraced property with connected guttering
I replaced my guttering 18 months ago with pvc coated timber and have had no problems
The landlord next door has recently replaced his guttering but has disturbed the joint with my guttering which is now leaking excessively.
My tenant has since been in touch to say she has noticed damp on the ceiling in the upstairs bedroom and by the back door.
I have tried to contact the landlord through his tenant ,but to no avail,
Have you any advice on what i should do next ?
many thanks