US University Has Hired Private Collection Agency To Retrieve Disputed Dues

I am an Indian student, I had accepted admission in 2015 to a US university. At that time I had intimated the college that I won't be joining via email. They had confirmed that the admission has been withdrawn and directed me to drop any courses selected. I did not drop the courses selected and apparently they have the rule that if you don't drop the course you are financially liable. I did not drop the courses at that time and suddenly in 2019, they send me a Legal Notice about pending dues for 2015 Fall. I had responded to the college directly disputing their claims and wanted to appeal for clearing it with the university since I never attended the university or leave India as a matter of fact. Now they have hired a private collection agency and they have sent me a Legal Notice asking to pay the dues. Do they have weight in their claims? I read that the statute of limitations is 3 years in India. Should I wait for them to legally proceed? They haven't called me or emailed me anything. Kindly advise.