@yusfu31 The Sims 3 Store site reads the same EA database as the EA App, so a code used in one place would read as used in the other. Does the base game show as owned on the Store site? If so, you don't need to do anything; the site should work as normal.
If the Store site doesn't think you own the game, the only way to fix it is to have EA customer support add the base game to your account again. Since you do own the game, this shouldn't be a problem. I would point out however that support doesn't generally help with codes bought from unauthorized third-party sellers, so if you mention G2A, you might be out of luck. Still, a valid code is a valid code.