How can I erase my account from a sold iphone ?

See this, What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support You mean that you did not erase your iPhone and the seller has had this for a year with all of your account info on it? You may need to wipe the phone if Find My iPhone is still active on the device under your Apple ID. Of course, the buyer may not appreciate you wiping the phone with their info on it as well.

Then without the phone, there is nothing that you can do. I suggest however, that you change the password for your Apple ID, as well as any other accounts you left on the phone. Why would you leave all of your data on a phone you sold, and then wait a year before trying to do anything?

If Find My is turned off, then it cannot be linked. The only thing is if you are using the same Apple ID, there is the possibility that iTunes and App Store purchases can be seen, but that would be about it.