@lkg4ansrs
Spoofed phone numbers (and "phone phreaks", the predecessors of modern "computer hackers") were common in olden times. I wouldn't be surprised if technical methods still exist to "borrow" or "fake" other people's phone numbers today. Though I honestly can't imagine how this would be done remotely, unless these calls/numbers are injected into or intercepted within the system from the "inside". Or it's just an innocent typo or an inconvenient billing error.
But on the device itself ... my immediate suspicion is that your phone is running some sort of spyware or malware. There's probably downloadable tools to clean it up, but it would probably be better to simply erase/reset the phone completely (after backing up anything you want to save). There's also task-manager or task-killer apps which can help you monitor and control exactly what's running "in the background", but they're not guaranteed to be fully reliable for this purpose unless you've rooted the phone and allowed them to have "full" priority (alongside the operating system itself) above other installed/running software.
But yeah, inform PM of the details, they may need to monitor or investigate (or report) some sort of potential abuse. And change your PM passwords - in fact change every password you've submitted through your phone - just to be prudent, probably unrelated to this other mysterious issue but it might halt potential problems you wouldn't want to deal with the hard way. Maybe request a new PM SIM card, too, again just to be prudent.
Their has been much talk about a "new" vulnerability called "SPECTRE/MELTDOWN" which could theoretically exploit phones with ARM processors in this way (and many other ways), but unless your issue is reported by hordes of people in the near future then I seriously doubt it's at all relevant. It's certainly irrelevant if the dates these calls were made are earlier than the date this (potential) vulnerability was discovered.
