Employment bond

I broke the employment bond with HCL Technologies and left to continue my studies. After 2 years, I got 2 letters in the span of 20 days from HCL Technologies asking me to send a demand draft of the amount mentioned in the bond within 10 days of receiving the letter . Both letters are written on HCL Tech letterhead. But they are not stamped and has a signature of a person (not printed signature, but literal one) who works in legal department of HCL Technologies. The letters does not mention anything about taking a legal action. But the summary of second letter is that, it is a final reminder to pay the money with in 10 days and failing which will be constrained to initiate appropriate proceedings as be advised. Can a company send such letters without the stamp? In a previous letter i received from the HR when i did not report to my work, they did not stamp the letter but they did mention that this is system generated document with scanned signature by authorized signatory and does not require the company seal. But for the 2 letters i received after 2 years asking me to pay, there is no such mention. Can you tell me how to proceed further and if the letters can be considered as legitimate?