Further to what (Cite Contribution), Saji, and other members have suggested, your primary issue at this point in time seems to be "how to handle the new company?"
Since you need to forward your resignation email to them and you have already resigned, just forward that email to them. Are there any problems in doing that?
Addressing Issues in Your Present Company
It would have been better if you had followed up your line "Please suggest what I need to do now..." with details of what you did.
Have you tried calling the HR, as a member pointed out? Have you sent any reminder/follow-up emails, which would also give you a record of your follow-up if and when you need it? If yes, what was the response? If no, why not?
Have you informed your Reporting Manager, since you are at the client site?
Have you updated the client? If yes, what's the response/reaction? The client ought to be more worried than you or your HR. You can also seek the client's help to push for someone to be identified for knowledge transfer, since that particular activity will be in their interest.
If you can close the gaps in the inputs you provided, the members would be able to give more relevant, practical, and actionable suggestions.
All the best.
Regards,
TS