Agreed with Beppi, earlier I didn't respond to your last query as noticed I have already informed you the possibility and what you could (should) do. As an employee you are bound to depend and believe what your employer says (they may lie or falsify or tell the truth). The best case ask someone (if you have any reference in Singapore) to visit MoM office with all the details ( please share the application details and other documents related to offer letter and online confirmation showing your EP approval without any further delay) to check what and where it went wrong.
But one thing you remember if MoM confirmed saying that they had issued the IPA letter to your employer then I'm very much sure your employer lied you all along and don't expect much from them rather look for a new employer (chances are almost nil that a MoM letter lost at employer's end). Hope you understood by now. Act fast. Good luck