Welcome to the parents discussion board and thank you for posting.
I see that you want to know how you can have your son who is now 13 years old back in your care.
It is not clear from your post whether there was any children’s services (new name for social services) involvement when you had your son. As you were only 15 at the time it is likely that they were involved. You believe that there was a residence order but have never seen it. Ask your mother for a copy of the residence order. You could contact the local authority area to find out if they were involved and could request copies of any records they hold relating to you and your son. Our advice sheet Access to information held by Children’s Services
explains the process.
If your son has not been in school for the last 5 years I think children’s services would definitely have become involved as the school would have reported his non-attendance. Unless your parents have decided to home school your son it is a legal requirement that children receive an education. You have parental responsibility for your son so can find out from his school about his attendance.
It is possible for you to make contact with the local authority where your son lives to inform children's services of your concerns. You should understand that if you do make a referral they have a duty to follow up on the referral and will make contact with your parents. They will then make a decision about what further action they will take.
For your son to live with you, you would need to make an application to the court for a child arrangement order. If there is already a residence order, you would be asking the court to discharge that order and make child arrangement order for you son to live with you in your favour.
As you do not have children’s services involvement and the application you need to make is a private law application, you will need to make contact with Child Law Advice on 0300 330 5480 for advice. Our service advises when children’s services are involved.
Hope this is helpful.