Bajaj Finance — After full repayment of Personal Loan, pending foreclosure fees of Rs56k became Rs6.86 lacs

I have taken a personal loan from Bajaj Finance in 2016 and in 1 year by 2017 I repaid the full amount. But there was a foreclosure fees they added which was 56k and I was not communicated this properly. I have not taken the NOC. Then 2017, 2018, 2019 and also 2020 passed. During lockdown and COVID 19 time at end of 2020, they started to call and harass and threaten in various ways. It was bad time and I could pay then. That time they said total outstanding is around 2.86 lacs. Now they are sending me a notice with outstanding amount of 6.86 lacs. Now I am in a situation of heart attack by seeing the outstanding amount of 6.86 lacs and now a days they threaten me like anything.Please help me.