I think your find that call was actually EE, that number Called me around a week ago regarding my current Loyalty Discounts, they had all of my EE Account Details without me having to give them anything other than 2 digits from Passcode as per normal ......but you never know.
On the Passcode malarkey, a common scam trick is where they ask for say, the 2nd and 3rd Characters then followed moments later, something like, No that didnt work, systems a bit slow today, lets try again, can I have the 1st and 4th Characters.
If you are in total doubt, as @chistery says ask for there Name and Dept and call back on a known EE Number.
