If people are reporting to you that you called them, but you did not, you are likely a victim of “spoofing”. This is a practice telemarketers use to disguise themselves when perpetrating a scam. This practice is indeed illegal and is called spoofing. They are not actually using your phone service and none of the calls they make go through your phone number. It is just them putting the number on their system so when they make a call it looks like its coming from your number.
Unfortunately it is not something we can do anything about. Its kind of like some one using your license plate number on your car – Ford could not stop anyone from doing that. Because its just a display. So your service has not been hacked in any way, but some one may be displaying your number.
You can learn more about spoofing here: