It's quite common to see mobile SIM deals for "New Customers Only".
Is this a case of qualifying only if …
A. No 'current' account with company XYZ eg having ported out from XYZ a week, a month.1 year previously or, a genuine 1st time joining.
or
B. Already have existing account but can still sign up for a 2nd additional new service and new number
Do all providers apply same "New Only" prerequisite - eg (A). or are some more flexible as in (B) ??
There no single answer to your question, you'd need to read the provider T&C's for each specific deal.