Frustrating leak

Help absolutely desperate for advice. I have a large damp patch in my hallway….bathroom is the other side of the wall. I had a new mains waterline put in as leak detection picked up high readings from that. The damp patch is not improving. Asked for leak detection to return and they have discounted any internal pipe work leaks. They have said the shower valve seal is leaking but the shower is the other end of the room. I haven’t been using my shower for over 2 months (as it was suspected the water from that was going down a window). I’m at a complete loss as to what is causing this leak. I’m getting to the point where I’m tempted to get someone to pull my floorboards up to physically look under my hall floor. Resisted that as leak detection had drawn a blank.. Am I being too impatient as the new mains waterline was done about a month ago? Any advice would be appreciated? I’m sick of this damp patch