I settled my SBI Card 15 years ago in May 2008. And have Settlement Letter along with subsequent col

I settled my SBI Card 15 years ago in May 2008. And have Settlement Letter along with subsequent collection receipts to support the same. However, in April 2023, I received a letter from Delhi Disputes Resolution Society asking me to appear before the mediation center located at Parliament Street, New Delhi, for yet another settlement. Upon arrival the employees of SBI Card concerned with collection were unable to provide a satisfactory explanation and asked me to settle again for 25% of the amount mentioned in the letter of DDRS. I denied proceeding because something didn't seem right. For instance, how come they're bringing this up despite proper settlement and that too after 15 years? What about the fact that debt is time barred, as stated in The Limitation Act, 1963. I'd appreciate if a professional lawyer can help me understand how to proceed. Thank you.