This is not your membership number. This is temporary acknowledgment number. This number shows that your form has reached at IEI and is being processed.
If you have not got membership even after about two months after applying, then
(i) either IEI needs certain documents which you forgot to attach with membership form
(ii) Your membership pack has been returned to IEI due to door close
(iii) any other reason. Pl call IEI, Kolkata at 033-40106266, 40106268 to clear this matter.
Do not forget to mention your acknowledgment number before your query.