Payment demanded by employer for 'Notice pay recovery' after 1.5 years of resigning

Hello, I am facing issues with one of big MNCs regarding a negative settlement. They are now demanding to pay 19k as they claim my full and final settlement is not over. However even though i provided resignation they never accepted it till the last date as per my notice period. i also extended my last working day to another month hoping they would accept my resignation. Unfortunately they never responded positively. Hence I had to leave the company as per the date on the extended notice period. After 1,5 years of resigning I was informally unprofessionally informed by a friend from the same company that i am liable to pay 19 k to the company. My friend forwarded the preceding mails from the company , as a part of official communication. Date of joining : Aug 2018 Resigned : Feb 2019 Probation period : 6 months Notice period served: 2months (1 month asked as per contract) I am quite sure that I have not breached the contract: I have resigned the company as per notice period . Please suggest me if i have to pay the notice salary recovery and get my relieveing letter.