The legality of extending probation period beyond six months

Hello.

I was working under DMCA free zone listed company for 8 months. I recently received a termination letter from my company.

The end of service settlement provided by the HR director is showing only compensation for my vacations and saying my probation is extended after the 6th month for another 6 months, of course without my knowledge.

My contract is limited and there is no clause in the contract about an extension option available. Is that legal? What am I entitled for as per the UAE laws?