Credit card dues recovery coercion from bank what to do

I was issued an AMEX UNLIMITED Gold card in 2012. However, my then employed requested me to transfer a payment of Rs. 4.25 lacs to a supplier with the promise of refunding me the amount which never happened. Thereafter, as the company closed, I became jobless for three years from 2013-2015. In the end of 2015, I got employment in an IT firm in Noida. Now, I am still working there. Recently, the bank tracked me using my PAN No. and called me up in my office landline no. I have no intention to be a defaulter as it is affecting my CIBIL, therefore, I proposed to pay the entire dues without any settlement but in installments as per my means. I have proof that after meeting my expenses, I cannot save more than 5000/- per month, therefore, I offered to start repayment @5000/- p.m. as a minimum guarantee and whenever possible I shall pay more to clear the dues as soon as possible. But the bank is threatening to pay Rs 5,24,000 within 3 days or face humiliation at your office. Please advise.