Builder Charging additional maintenance.

Builder had asked for one time maintenance charges of my flat at the time of making final payment of my property. during the said payment process he also promised me to submit the affidavit even before complete my internal required basic denting & painting i.e. huge leakage in entire flat, due to seepage the whole wall painting got affected, didn't even provided the basic bathroom & toilet damage repairing work. since he has cooperated me during the payment process of my purchased property I handed over my affidavit stating the builder has completed all the pending work. the very moment on receipt of the said affidavit he drastically changed and stopped the internal work and i shifted in the flat in as it is conditions since i was having no other option to resort. since i was doing frequent followup he kept on promising that the pending work shall be done in the due course but he miserably failed. subsequently the society was formed & i am paying due maintenance charges to society regularly since its formation. now all of a sudden he sent me a demand letter stating outstanding to be paid immediately with threatening the dire consequences if i failed to make payment. i urge for your guidance on [deleted]/ Mob [deleted]