H1B transfer while other transfer is pending

Last month my H1B Visa transfer (premium) was initiated from company A to B (May 9th 2013) and started working for B with Receipt number and got two pay checks.
meantime I got RFE on May 21st and transfer is pending status now.

I got good offer from previous employer (Company A)and planned to join back.

Question: shall i work with I-797 of previous employer (Company A) or need to get new H1 transfer for A once pending visa transfer(Company B) is done?

Thanks in advance.

You can work on A’s petition if it has not been withdrawn and their I-94 is still valid. You can ask B to withdraw their petition (financial loss to them) or see if it gets eventually denied after RFE.