Circle with line through it where mobile data bar should be

I was on a call with my mom then all of a sudden it hangs up. I try to call her back, but no ringing happens and hangs up again. I don't understand why I wouldnt be getting signal if there's cell towers around me. I will check my sim card soon and make sure it's sitting properly.

I was on a call with my mom then all of a sudden it hangs up. I try to call her back, but no ringing happens and hangs up again. I don't understand why I wouldnt be getting signal if there's cell towers around me. I will check my sim card soon and make sure it's sitting properly.