I got mailed a card saying Im registered to vote, but I never registered. Any ideas why? how do I unregister?

I just got a polling card delivered (Im in the UK) with my registration number, but Ive purposely never registered as I dont want to vote, and I dont want to be on the electoral register so I dont have to do jury service (for personal reasons). is there any way may parents may have registered me and forgot to mention it?