please tell what devices I can use at home to record my phone conversations?

there are some machines for recording telephone conversations, look for'em on stores like radio shack

I say: extremely than going a criminal offense and recording calls, ask the series companies to get each thing in writing till now you deliver any money. so a strategies as your son's mom, nicely, recording the calls won't help you notice them. The courts are the area for that.

put them on speaker and use a recorder