Can a phone number be hijacked?

My mother just got a phone call from her own number. Awkward. And now she can’t access her voicemail because she now needs a password to get to it. Not sure how this is possible but the number is exactly the same. But the voice on the phone when she answered the first time sounded Indian/Arabic. They even asked for my mother by name— and pronounced it right! Knew that she was having chronic pain, too! I’m starting to wonder what the hell is going on here...

Any thoughts? The phone is an iPhone 7, in case that helps....

Update: questions answered, thanks for your input. This was apparently a social engineering attack on my unsuspecting mother. Be cautious about phone calls from your own number, and always be evasive when answering any questions that could either be answered with yes/no, or reveal personal information. My mother was lucky she knew how to handle scam callers, but other people might not be so lucky. If only you could block your own phone number. There’s no reason for you to call it, after all. Unless it’s the only way one can access their voicemail.