H1 B transfered but old I-94 number

[MRH1BB]

I have issue where ,i got my H1b transfer approved and i did not get a new I-94,but the I-94 number mentioned in my approval mail send by USCICS is same my old I-94.What i should do?.My attorney is asking be re -enter the US on the New H1B petition.

How many days before the start date i need to re-enter?

if i re-enter using the new H1B petition,can i still work with my old employer and serve the notice.?

Can i go to nearest border and re-enter,i am in SFO?.

I am confused.Please let me know teh issues.

Please guide me.