Any system can be hacked. Some take more effort and time however, none are completely secure. Each provider will offer tips as to how to try to prevent this.
A Spectrum customer had this happen not to long ago and was surprised to find in his contract these dreaded words, "Customer is responsible for any fraudulent or unauthorized use of the voice service that occurs through the subscriber's account regardless of who is responsible for such usage."
Not sure why you're concerned but, check the fine print in your contract, regardless of the provider. If you suspect something, get on top of it quick and let your provider know.