Sounds like you are a victim of domain theft. If you share the domain name, maybe people can help. If not, it's hard to take action.
In general, if your registrar account was hacked and your domain was transferred, then sold and transferred again, it is possible to get it back but not easy.
Consider sharing more details. You have nothing to lose at this point. Other people that have had this happen have shared the domain name. It's the only way people can give help.