Parking lot issue - Apartment

Hello Layers, I am facing parking lot issue in our apartment. When i booked my flat..the builder told my parking lot as position A ( part of entrance area ) . During the time of occupancy he told me that position A is not available since this belongs to the owners at the entrance area. Then he allocated a parking lot lets say B. We moved to a new flat by Nov 2012 and there was no issue with the parking and we formed a home owners association but either builder or we have not marked any parking area permanently. There were 2 unsold flat at that time. Nearly 8 months we stayed there without an issue with the parking space. Another owner ( who came late since he owned one of the unsold flat ) who came after 8 to 10 months started parking in our parking space claiming that the builder sold his apartment telling that the parking space of mine Parking space B is his parking. Till now there is no marking done on the parking space. How can i go ahead legally to solve this issue and get my parking space B. Thanks and best regards Dileep