Road Issue In Society Blocked By One Plot Owner Causing Issue Connecting Road

I am living in a society, where row houses are situated with common plot. our plots are situated in such a manner that, we 4 shares the boundary (A, B, C, D), A and B plots are road facing and we (C and) are behind situated to them. we have received a small pathway of 10-12 feet, where C and D plot can use to connect road and carry their vehicles. However, the plot owner of A has kept obstacles on that common area ( flower pots, bricks, etc) claiming that the area belongs to them. Plot A and C is common and B and D is common as per govt document. our society is legal and everything is official. The road which we have received is also approved in the plan, however the plot owner of A is chairman of the society and he is not addressing our concern. We are facing this issue for the last 20 years. What is the way to remove those obstacles? what punishment can be given we are facing a very bad situation, and as he is chairman and his relative (who is also part of some other plot is treasurer).