Give them your registration code for the game to prove you actually do own The Sims 2 and the adviser will add The Sims 2 Ultimate Collection to your Origin account.
Tell the adviser you have a physical copy of The Sims 2 and would like to go digital. This isn’t a tutorial on how to get the Ultimate Collection if you don’t already have it but in quick terms, if you have a physical copy of The Sims 2, go to EA Support and go to their live chat to speak with an EA Adviser. The nifty thing about this is that even if you own the base game and nothing else, you get the Ultimate Collection for free. The Ultimate Collection includes all expansions and stuff packs ever released for the game, including Holiday Stuff which was a limited edition stuff pack and now goes for around $200 on Amazon due to its rarity. So the big news recently is that Origin is giving away The Sims 2 Ultimate Collection to all Sims 2 players.