thought i had done my SEP revalidation last August 2013
Did you do a Proficiency Check?
In which case find the same Examiner and get them to sign your Rating entry?
NB: Still not legal to fly until you do.
Or do you mean you completed the requirements to revalidate by experience
but then didn't (due bad advice) do the administrative step of getting an
Examiner to sign your paperwork.
In which case you will need, as others have stated, a course completion
certificate and then to pass an LPC with an Examiner to get your
paperwork signed and renew your Rating to become legal again.