Is the undocumented salary increment a part of the basic salary or allowances?

I am currently employed by an engineering company since the beginning of 2014, and I have received termination notice in mid-2017 (+3 years service).

The initial full salary with the housing and transportation allowances was AED 20,000.00 and I have the breakdown of the allowances (basic salary, housing and transportation).

It was then raised to AED 30,000.00 in 2015 and the employer simply started to transfer the amount of AED 30,000.00 to my bank account without giving me any revised contract with the new payroll breakdown of the allowances.

Also, the employer never updated the Labor contract with the revised salary of 30,000.00 AED leaving the gratuity computation now open to many ambiguities. I have filed a complaint with the Ministry of Labour to seek advice on my rights.

What would be the best approach to determine the basic salary, housing and transportation from the AED 30,000.00 salary, as this information is now omissive?