I feel your pain. Unfortunately when auto dialer programs and ‘burn phones’ so easy to get, anyone can program their computer to spend all day dialing.
Area codes are published and well known, so are prefixes (the first three numbers) once you know that just program the auto dialer to dial from 0000 to 9999 and you are set to go.
I for one don’t answer calls from numbers I don’t know anymore because of it....and can it REALLY be my last chance to lower my interest rate? Please?????
Anyway, if you get that popup again, do as desribed to remove it from your device and you should be fine. On the upside, getting those popups on an iDevice is usually just an annoying inconvenience vs other devices where the nasty code can actually run and become a bigger issue.