Obviously, they are using you as a quota, just go look for job, make it seem very obvious you are looking for job. ask for 2600 increase OT, you just need a place to go 1st, then approach your co for a counter offer of not less than 3200, (this is considered low, given you are working 13hours), you basically earn lesser per hour compared to an ITE working shifts.

If you leave, do singaporeans a favor by refering that coy to MOM and see what they say