Can a employer send a legal notice in letter head

When the person have asked my F&F and Reliving letter to the previous employer, he took that person full address and sent a legal notice to the person for the below points: 1) It has been brought to our notice that XXXX, has been inaccurately stating, tenure at XXXX during job interview process in other organizations.: Can you all let me know please if a person not giving resignation and employer also not terminating it will be counted as working only? so i can produce it as my work duration only? 2)After asking to do the F&F formalities can a company do this kind of illegal activity? 3)Can the write wrong details in that letter: ***You were issued a warning letter both on your official and personal email id on 25, October, 2019 for 9 days of unauthorised leave within 3 months of your joining. There was no response issued by you to the warning letter: NOt RECIVED ANY MAIL ****You have failed to sign and return NDA which is mandatory at XXXX: NOT GIVEN ANY DOCUMENT TO SIGN ***You have failed to follow protocol of leave application in spite of verbal and official communication: NO INFO *** You have failed to communicate the daily work status email regularly.: DETAILS ARE THERE BUT NOW THEY HAVE PUT WRONG ALLEGATION ***You have failed to attend the evening team meetings on a regular basis:DETAILS ARE THERE BUT NOW THEY HAVE PUT WRONG ALLEGATION *** You have not conveyed the location of cloud storage where work related to network captures are stored :DETAILS ARE THERE BUT NOW THEY HAVE PUT WRONG ALLEGATION