Neighbours complaint on my house window

We have 720 sq.ft area. We constructed our house within my area but not as per plan approved by municipality. Now my neighbour complaint to municipality and they are saying close window and continue construction but we didn't agree so they sent a letter and told to sign as we aren't constructing as per municipality plan and now we got 2nd letter and again they are telling same. What should I do now? what happens if I take more letters?