My ex-partner has informed me that someone came to my old home with a summons - well I pressume that's what it was.
Who do I contact to find out what is happening. As I do not know what this could be about.

Do you have an idea what the summons might be about? You would have to check with all the courts covering the area.

You might also try googling your name and see what comes up.

... You would have to check with all the courts covering the area. ...

Problem is, it could be a court anywhere. Assuming you are in the U.S. living in State X, someone in State Y could be suing you, in either State X, State Y, possibly some other state; in either state court or in federal district court.