Leeking pipe

Okay here I go tried to contact my landlord over simple mater but dose not reply back. Water leeking fast mode time to time back of block of flats. Tried contacting seven Trent but they can't do any thing because it's a private pipe. It's not my toilet but someone else. Been leeking for about three years at the back on our flats (toilet pipe overflow). Don't know what else to do?. I could try other resident's but but don't think will help because still leeking. Could put a note through the letter box but again could be ignor. Quite bad now the water getting onto the brickwork. Thankyou any replys.