It is not uncommon for companies in Qatar to have a company policy to make certain contractually agreed payments only after the probation period (usually 6 months) has been completed.

Defies all logic but this is how things are here. For instance, furnitute allowance contractually agreed may be paid only after 6 months of joining. And should the employee live w/o furniture for six months ?? :p

Anyways, my suggestion to you is to have patience, if they say they will pay it after 6 months, then wait for it.