The relevant law is in the Fourth Geneva Convention of 1949.
UN resolution 497 from 1981 is pretty clear. And before anyone states that it is only the UN, Israel exists because the UN created it.
If Israel is disputing the laws of the organisation that say Israel has the right to exist, then Israel is disputing its own legitimacy. There are nations that do not recognise the right of existence of Israel, Israel being one themselves is not a sensible position to take.
Israel should accept the Golan Heights are not theirs, but just never give them back, keep fudging it and saying the time is not right - that solves the security problem for Israel and does not put the US, or any of the other Israeli allies, into the uncomfortable position of having to denounce Israeli statements of ownership.