I had exactly the same thing a few weeks ago, a call, supposedly from Orange, which offered a free phone upgrade and 10% off line rental . I've been with Orange for years and previously they have phoned to offer a loyalty bonus of £50 taken in parts off the next 3 or 4 bills. First time I was suspicious but it proved OK and has happend in subsequent years.
Consequently I went ahead BUT specifically said I didn't want an upgrade, I was happy with my phone."Have it anyway", they said, "you can always sell it on Ebay"
Then I get a call saying I can't do this and stay on my current tariff! - WTF! anyway I agreed a new tariff and waited.
2 days later - the phone "upgrade" (worse spec than my current phone, no camera or anything!) arrives along with a letter saying that the new SIM {WTF! - again} in the package will be enabled in 3 days time - WITH A NEW NUMBER!!!
This was a complete con - the call, phone and letter were from "The Mobile Phone Company" in Blackpool - NOT from Orange.
I wrote a stinky letter telling them how they had lied to me me, mis-represented themselves and better not proceed with changing ANYTHING and sent the entire package back to them by Royal Mail Special delivery.
I then called Orange to find out what was going on, to make sure any changes arranged on my behalf were cancelled and filed a Dealer Complaint report with them.
Can I suggest you call Orange straightaway and do the same.
On the Orange website you can find out about any offers due to you as a good customer and yes I could have 10% off my line rental but no need to have a new phone, or SIM or number!
These f*****g cowboys should be hunted down like the lying dogs they are. I asked several times "are you calling from Orange" and each time he lied and said yes!!
LCDMAN................The man with no sig!