Bank refusing to give back property documents

Sir my father has taken an housing loan from bank in 2000 and repayment schedule of 14 years with intrest the lone was on variable intrest and we have paid all the EMI on date with no bounce of check the lone was completed in 2014 when my father went to collect the documents they refused to give stating that on variable intrest u have to pay additional amount as an intrest which u have not paid my father asked them why they have not intimated before i could have transfer to another bank which is comfortable to me they had int intimated in any way either on phone (or) letter may father refused to pay as there is no outstanding EMIS Then later after 1 month again my father went to pay sum amount and settle the issue but bank refused to do so the sum of amount is inr 30,000 as an intrest for total for that they had kept the document for this many years my father had expired 1 year back so i went to bank for repayment and to collect the documents now they are asking to pay 1,60,000/- i asked why so it was only 30000/- they said that is intrest on 30000/- till now i argued so now as a settlement bank is asking fr rupees 80,000 as a one time settlement sir please tell me what can i do on this matter can i file a case on the bank for putting intrest on intrest my email id is ([deleted])