There are various reasons for a domain to open a wrong website but the two most common are – incorrect pointing of the nameservers or domain name expiry. You can check these details through any online WhoIs search like this one.
1. If your domain points to the wrong nameservers, you can change that from your domain management area with your registrar.
*Note that changing of the nameservers requires a propagation period of up to 48 hours.
2. If your domain has expired, you simply need to renew it with the registrar.
Once renewed, there is a short propagation period of up to 24 hours again.