A few months back I lost my phone, so I went to my operator with passport to get new sim with my old number (in Thailand) . She said the sim isn't actually in my name but my ex-girlfriend's, and I told I remember I took the sim with her id as I didn't carry my passport with me, so I guess there's nothing I can do.

She just replied well we could change the sim to your name, didn't even check with the original owner and 5 minutes later I was on my way with new sim.