Please corret my sentences

This to inform you that Mr. X , one of our staff members was not present when asked him to do the emergency work during weekend holidays.

He has already received sevreral verbal warnings since he joined the company and followed by a written warning on [date] because of his unreasonable behavior at work but unfortunately no improvement has been shown to date, and also now he started new behavior like not being present for long days without inform / submit any medical certificates.

No other course of action is available to us. It is, therefore, I am reporting you that I decided to dismiss him from his job of XXXX