i was adopted when i was seven and my last name on my birth certificate was never changed
Family Law Attorney
If you are under 18, your mother or father would have to take care of this. If you are 18 or older, go, in person, to the Clerk of Court where the adoption took place and explain your problem. Have identification with you. Hopefully, this involved only a glitch in the paperwork that can be fixed. If not, the situation can be resolved with an attorney.
This response does not creat an attorney client relationship. In all cases, I recommend you seek a paid consultation with an attorney with expertise in this area.