Q: Call Ended as soon as it rings...

Hi

I am having a problem with Call Ended when I dial a number  but, it doesn't happen every single time. I tried it with different numbers and if there is an automated menu I am able to choose the numbers to get to who I want to talk to but as soon as it rings, I get the Call Ended. In other occasions, it's not a Call Ended but rather, I get nothing from dialing the call, there is no ringing, its silent yet the call is active with seconds increasing. It makes no sense.

Other times, the Call Ended occurs when I am in the middle of an important call with a customer service representative and then I would have to call again to explain myself to a different person which is so frustrating. 

I reset the Network settings, held the Home and Power buttons but it made no difference with the same thing keeps happening.

I am wondering if this has anything to do with my internet connection?