google business profile keeps rejecting our new phone number

Ring the number yourself from a mobile. If it lands on a phone menu, a recording or a call centre, Google's check can fail, it wants it to reach the business. Also set a voicemail greeting that says the business name, helps if they call to verify.

Is it a local number or a virtual/VoIP one? Google prefers a local number that clearly belongs to that location, and some virtual numbers get rejected or flagged. If you need call tracking, put the tracking number as an additional phone and keep the main local number as primary. Also put the new number on your website and update it on the other big listings first, so it matches when Google checks. Phone changes sometimes trigger re-verification, so don't change it back and forth, that makes it worse.