Even if it was on the list of EE Partners, forging CLID is a trivial process that scammers use routinely.
I'm pretty sure nobody from EE would cold call you prompting you to upgrade. Without knowing further details, I smell a rat here. This sounds like the classic scam, where you to agree to an upgrade, the scammer then orders what *they* want but in your name. You end up receiving something you don't want, so you call the number given to you by the scammer, who tells you to "return" the item to the "returns" address (*their* address in reality). So you've just signed up for another 2 year contract with a device that you don't want and have just posted to the scammer.
