Legal notice received from my previous employer

I had signed a contract(only on company letter head) for one year with a start up which was from May and i left the company with any notice in the month of November. I was suppose to give two month notice period but the company was not paying my salary on time and at times we have to got the salary for two month in cheque and the same has bounced in the bank. Now the company has sent me legal notice saying that i have have not served two month notice period. While leaving from the company have left my laptop, phone and charger at my desk at my company office, but now in the legal notice they are saying that still have the company assets with me. Lucky i have the images with location and call recording for the same that i have submitted it. Please let me know what shall i do