Passage rights from neighbour's land

We have a passage rights of 6 ft, but many years back neighbour's constructed g+2 (3-4 ft elevated from ground) but they gave 6 ft access on ground floor but :

1. have constructed 1st & 2nd floor balconies above that 6ft access passage.

2. have also constructed a tank underneath that access path.

My parents and neighbour's were friendly then.

Now we want to have parking in our building such that atleast 2 wheelers come from that passage, and want to have their elevated path lowered and the tank removed. But they are not agreeing to anything.

What rights do we have?