Credt card from 2007/ HSBC

Portfolio recovery called me about 6weeks ago saying I had a debt charge card from 2007 @ HSBC in the amount of $350 I returned their call as my mother had said to call and give my mom authorization to talk to them as she was going to pay debt -they never called me again and nothing has been paid - my mom thinks they are a fraude - I have had some credit issues but now I am beginning to think they may not be ligimate how do I know if they are ligimate?