Remedy when two adjacent flats has been registered with same number

I have purchased a new Flat registered on 09/12/2015. On the same floor, there was 4 Flats, 2 already sold out, bearing number 2A and 2D. As the Master Plan provided does not contain any Flat Number, I could not verify the correctness of the Flat Number. I had changed my residential address to the new one in all relevant documents like Voter Card, Aadhar Card, Banks, LPG etc. The 4th Flat on the same Building and Floor was sold out on Dec 2016 and it was sold with the same number i.e. 2C. Thus, now we have 2 Flats with number 2C on the same building and same Floor. It is clear that one of the two needs to be rectified. My question is which one needs to be rectified?  Is it that since the registration of my Flat was done prior to the other it will remain the same and the other needs to be rectified or it the Promoter/Developer who will decide, that which one needs to be rectified. What legal remedy do I have?