Ive got cast iron guttering, and next door as pvc guttering, next doors gutter comes over my property and where its joined its leaking into my bedroom above the window its caused so much damage and damp ive got to get the full wall in my bedroom plastered, ive spoke to the landlord (grant management) they said its not ther problem because they bought the property after the guttering was replaced they did come out and put flashing under the join but its still leaking please help