How to use the previous company Priority Date

[vbr]

The company I'm currently working have completed my Labor and I-140 (approved). Because of H1B six years limit and before the new law came into force I have returned to India and working at company branch office in India.

Problem is...now the company is not willing to continue my GC, how can I use my previous priority date withought the present company co-operation ( for documents), to join a new copany and to continue my GC processing. Please let me know my options.

Thanks in advance
vbr