speedwoten
The CAAS can accept, or not, all and any licences from all over the world, they can also accept these same licences but reserve the right to impose certain limitations if they consider the experience or academic aspects of their own licence are not equalled or exceeded by the foreign licence they are being asked to consider, (yours).
As I understand it you have command time on a B737 and F/O time on a B747? Your total hours do fall in the required total minimum for SIA but you do not have the required breakdown of heavy jet/wide body command time. No one is playing games with you, either you meet the employers requirements, (SIA's), or you don't and they wont be bending their rules for you as your experience doesn't even come close to their minimum requirements.