Sounds a nightmare! Regarding them overlooking your garden. A block of flats in London has just won an appeal to stop people using a viewing platform at the museum, because it means members of the public can see into their bedrooms/living rooms.
I don't know what the long-term solution is going to be in the London case but, maybe if you are losing the light anyway, (which I thought they weren't allowed to do), you could ask the planning committee to insist they put up some form of screening such as tall trees or opaque structure to prevent 'peeping toms'.
If you have access to the plans, it may be worth employing a freelance building inspector to check they have been passed to the correct rules. My FIL had a builder wanting to buy a section of his garden for 3 bungalows but when we checked his planning application he had submitted for only 2 bungalows. This was the application that was passed. We then found out he was trying to buy land from next door with the intention of building a total of 6 bungalows under amendments to the original plans. FIL refused to sell his land so the whole lot was scuppered. Builder not happy but nothing he could do about it.