EP pass

Company B is obliged to cancel the EP application if its basis (your willingness to work for them) has disappeared. Thus by right they should have cancelled right after you told them you don't want the job any longer.
If they don't, you can inform MoM about this (and submit written proof), so that MoM can cancel the application.
But in fact, in your case, you don't need to do anything: Your current EP with company A remains valid until company A cancels it (which they must if you stop working for them) and company B cannot do anything about it. Even if you are eventually given an IPA (In-Principle Approval) for your EP with company B, some action from your side are still required (i.e. accepting the IPA and resigning from company A) before this becomes an actual EP - as long as you don't do this, no harm can come out of this.
(However, you cannot apply for another EP, e.g. with a company C, while the application of company B is still active - but in your case that's irrelevant, right?)

Thanks friend for the information,In this case do I need to pay the one month salary to the company B?,because I had signed their offer and informed about my dis intrest in the opportunity on the same day of submitting the relevant documents for EP processing.Please suggest.

-Lisha

If you signed an agreement with company B, you have to fulfil that agreement (e.g. if it says you have to pay a penalty if you resign within the first year, or any other period, you have to do that).
But this has nothing to do with EP.

Thanks Mate for the guidance,but will it hold true as the clause says my appointment is only subject to my employment pass getting approved and I join company B on desired date,as I am requesting company B to withdraw the application from the day they applied EP but they are not ready to do so.

-Lisha

Well, you agreed to pay the penalty in that case. Nobody forced you to sign that!
("EP getting approved" means IPA granted)

Edited to add: The company is right, in my opinion, to ask for the penalty, since you are not willing to fulfil your part of the agreement you signed. If they sue you, it will get messy and cost you a lot more (I am pretty sure you'd lose), so I recommend you talk to them and find a mutually agreeable solution.

Thanks Beppi for guidance and suggestion

Hi Friend,

Company B had sent me the copy of IPA,though I already ask them that I am not interested in joining them and they do not show any interest in conversation of cancelling the new IPA nor further talks when I contacted them,will this IPA auto expired as it mentions 6 month validity and will it have any impact on my existing EP from company A as I am continuing my job with company A(my old employer).

can I travel outside singapore and come back in on same old EP of company A

-Lisha

As it says, the IPA expires after 6 months. It will not affect your current EP (unless you have the new one issued, in which case the old EP is cancelled) or your ability to travel in and out of Singapore. You can just not apply for any other new EP while the IPA is atill valid.