My neighbor have had their boiler flu moved. It’s now on our property. We live in a terrace house and we have a shared gennel. I’ve told the builder politely to move it but they rudely replied “no it’s staying there” and are adamant is not moving. In the photo our property is on the right and if you look up to the guttering you can see were our property finishes.. What would be our next step to get him to move it ?