How do I get rid of unwanted subscription?

No because your details are on that site, probably in your name. If he has used their services, they are demanding you pay for them.

Unfortunately the law is on their side. However having said that, it depends in which country the site is and the laws pertaining to that country. If it's a UK company then UK law applies. If it's outside the UK then they would have a problem to enforce it.

Before you do anything find out where they are and send them an email explaining what's happened. I wouldn't hold your breath though, because any site like that any explanation doesn't cut any ice with them.

A system restore, restores the PC to an ealier point in time. It cannot, however, turn back time. Your ex has purchased pornographic material in reality, so turning back the clocks on the PC unfortunately can't retract any financial transactions made. I would suggest contacting the company and telling them what's happened. Also contact your ex and give him a bollocking.

No, it will not you will have to get in touch with the company that is billing you. You need to talk to a company rep. I would also send a certified letter to them. The info you need to get in contact with them should be on the statement or you may have to visit their website to get contact info.