mass effect 3 code already in use

If the disk is new,that means the code is already being register by someone else,go back and get a new code from the retailer.Code can only be register once to an Origin account !

As for your issue, the "code invalid/used " message means the code is already registered to an Origin account. There can be number of reasons for this.

Did you purchase the disc online? Used? The game code is only redeemed once. After it has been registered to an Origin account, it becomes used.

Did you enter the code and nothing happened, then reenter it? This can be common for DVD installs. If that's the case, the code has been registered and you have to wait for the game to be activated (the game entry shows up in your My Games library) before the install will continue.

1st Make sure you are logged into the account on which the game/s were registered.
If you're getting the "code already used" message, it means the game code has been registered.

Please make sure you have "Show: All Games" in MY GAMES selected. Have also a look at "Hidden Games" because manually hidden games will not appear in the "All Games" view.

If none of the above, you'll have to contact a game advisor (accounts) via live chat from your computer to check the status of your account and where the game code may be registered.

Origin client Menu:
Help > Origin Help.
Live Chat link, up top next to the Search box.
or here..

1. Click the link https://help.ea.com/en/contact-us/ask and log in with your Origin name and password.

2. Where it says: ’What Can We Help you With’, type in ‘GAME NAME’

3. Click Find Solutions

4. Select "Your problem,eg accounts" from the drop-down list and also select your platform from the list.

5. Click: Find Solutions

6. Scroll down a little and on the lower right hand side, Click "I Still need Help"

Picture to help you understand better,  https://help.ea.com/article/welcome-to-the-new-and-improved-ea-help-center

The Window Will Open...
You’ll now see the currently available contact options. These may vary depending on your geographical location and the time of day. Phone or Live Chat are the best options.

For customers in North America:

• Select "Call me."
• Enter your phone number.
• Select "Submit."

For Customers outside of North America:

• Go to the "choose a contact method" section
• Contact us using the telephone number provided within the listed opening hours

Please be aware that it is likely that the agent you speak to will need to confirm information on this account.

Hope this helps
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***Please note...I do not work for EA/Origin. Questions belong in the forums,Solution is like medicine,same medicine/solution may not work on same problem

I don't answer questions via PM.  AHQ is "Player-to-Player" technical self-help forum