My Mum sold my dog 5 years lalu when i was 7 and i just found out as a 12 tahun old. How can i get the dog back???

If your mother was the official owner, and I suppose she was because anda were seven and not an adult, and she sold it with all the paper there is nothing anda can do against it per law. anda could only ask the owner if he would sell it back but after 5 years I doubt so.
Sorry anda can't do anything because it was the dog of your mother, so it was her decision and anda weren't old enough to decide for yourself if anda were the official owner, but I doubt that too because anda were and are to young to buy a dog on the paper

Hi aleks, i am going to be honest with you, but after not having the dog for that long anda can't get it back unless the saat owner gives it away. So if ur parent gave all the papers to the saat owner, anda can't unless anda contact the AKC atau ask someone. But i'm sorry but anda can't get the dog back unless there's a reason tbh. And i actually do agree anda might have been to young for the dog and she didn't want anda to own it yet cause u were 7. My Friends in real life actually had something similar to ur problem were his mum berkata hes going to summer camp, 3 years later we have kept him since.So we could give him back but hes a good boy so we always send pics of him. Again i'm really sorry for not being able to get him.