my drainage outlet opening into a drain can is blocked by my neighbour

My drainage outlet is blocked by my neighbour. It opens into a canal tat runs across my boundary. All d houses adjacent to mine have d same system. It ws so ever since i bought the house. He is threatening me saying that the canal is his . Its atleast a 2 km canal while he jus occupies three cents of land on its other side. Am a widow and they have been harrasing me like this. Last rains my whole house flooded for there was no outlet for rainwater as they blocked my pipe. Now i m making a pipless dranage system so they cant block it and the are threatening the workers and me . What should i do. They drink liquor and fight so there is no reasoning. Who owns a drainage sytem? Can it be privately owned?what are my rights. I know that this land belonged to another person and the present neighboursd worked as his labourers who then gave them this land for free. How do we find the ownership of a drain.