First of all, don't "panic for your certificate". Even if you never access the MCP site, if you passed your exam it is safely stored and you won't lose your certification.
As to your access code. maybe the email message got lost for some reason. The best thing to do is to get in contact with your Regional Service Center (RSC) either by phone or by email. In the past, I've always found them to be very helpful, and they
are usually able to fix these issues very quickly.