Is it just a matter of ringing 789, and they'll reinstate my original number? Thanks.
"original number", are you a pay monthly customer? Did you call / go online to upgrade your existing SIM?
If so the new 4G SIM should just replace your existing SIM with the same number.
Unless you purchased a new 4g contract, in which case your 4G SIM will have a new number (you may also now have two contracts).
I would give the Team a call on 789 to find out what has happened.
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