Concerns in Buying a new house

Good day. I sold my 1Bhk flat post 14 years of occupation and brought a 3BHK flat in an under construction property in 2014 on the 42nd floor taking care that the money taxable under capital gains Is invested completely into the new property. During sale the verbal agreement was that the possession would be in August 2017, however when agreement with builder was finally done in 2016 the possession date given was Aug 2019. Presently now in Nov 2020 it is brought to the notice that The builder would build only 40 floors and the possession would be End Dec 2021. Since my floor is not going to be constructed he has offered the following: 1. Shift to new apartment within his project. ( this is not meeting my main criteria of view) 2. Or take refund with 9% and come out of project. My concerns are as follows: 1. In case I want to come out of the project, how can I best leverage The amount I would get on my payments to builder Since interest component is taxable and does not take into consideration for the huge EMI I already am paying on home, insurance and other fees paid. 2. Capital gains, don’t know how this will be calculated now against the agreement value. Can I leverage this option, would it be good. 3. If I stay in project are there any implications as my agreement would change as against my earlier one. Any implication from bank, IT, capital gains etc. 4. Anything I need to be wary about. Thank you very much. Best regards, Kevin