Flood & other problems from upstairs

fiddle290

I am one of two leaseholders in a converted house, I'm downstairs.  In August my upstairs neighbours had a new bathroom installed and sadly I was away.  When I returned after 3 weeks I was greeted with sewage down my hall and all over bathroom.  I was devastated as my bathroom is no more than 12 months old.  All maybe sorted but I didn't go through insurance.  I ended up paying for cleaning and replacing some items, slight repairs.  I've had to park it but will be taking up issue with plumber who refused to give liability insurance and also turns out he was working for cash in hand so he could claim sick leave but that's another issue.  

My current problem is they have installed an outside tap below my bathroom window and above an air brick to it without discussing it with me.  The side of the house is shared pathway, they have access via it to their garden and the outside wall is to my property.  The tap is connected to a plastic pipe, not insulated, running down wall from their kitchen.  My bathroom privacy is affected but not only that, the pipe will freeze and cause issues.  It wasn't discussed as it should have been but more importantly will cause more problems for me.  They are unreasonable and will not discuss with me my concerns.  What can I do?