Phone call still active even after hanging up

I was talking to someone using my phone on my iPad and then I called someone else on my phone after hanging up on my iPad. When I called at first on my phone it said call failed and but I could hear the person. And when I called again and hung up but I could still hear them in the background. I didn’t know what to do so I turned of my phone and I don’t think the person knew I could still hear them.