What to do if the employer counts overtime as regular hours?

Hi

In Oman, under Oman Labor Law, my contract has the basic salary of 45 hours which is fine and in line with labor law, but there is a second line which states "Additional Hours".

We work a 60 hour week so that second line "Additional Hours" is basically 15 hours. The issue is the hourly rate for the 45 hours is the same as the 15 hours no change or an added minimum of 25% to the overtime hours as stated in Articles 68 & 70 in the Oman Labor Law.

I have requested the company to backdate and correct this but they are ignoring me, do I have a claim or are they correct with a fixed hourly rate for a 60-hour minimum working week?

Thanks for your time (My position is Materials Manager in the Oil and Gas sector)