بسم الله الرحمن الرحيم
(1) Changing the religion and signing on the affidavit for the marriage is diversion from Islam which is severe crime and major sin. It is necessary for you to do taubah and renew your Iman (faith). So if you were repented your previous practice and did taubah and read Kalimah Tayyibah wholeheartedly then your nikah was valid with the Muslim person as per the Shariah. It is lawful for you to maintain the marital relation with him.
(2) It is not correct for your husband to call you a Hindu on the basis of your past. It is also very bad to call any Muslim a Hindu. He should do taubah and should avoid saying such words. However for his further satisfaction he can ask you for the renewal of your Iman i.e. you should read the Kalimah Tayyibah and Kalimah Shahadah with full belief that Allah is One, and the holy Prophet Muhammad (pbuh) is His messenger, and you should believe on the day of judgment and then solemnize your nikah again i.e. perform your nikah in the presence of two Muslim witnesses. Thenceforth both of you should start living your life as per the Islamic teachings.
Allah knows Best!
Darul Uloom Deoband