Can I activate AppleCare Protection Plan after warranty expired?

Additional thoughts (after edit period expired):

Depending on your country, the old plan may still be available (it is no longer available in the US), but the requirement to register it within 364 days of purchase of your computer still applies, so "buying" it within 364 days does not work because you are buying a box which is worthless without registering the code inside with Apple - you have to register it with Apple within 364 days. If Apple insists that it is too late (as it appears according to their rules), then I would ask for a refund from the seller. And, even if you bought it from an authorized reseller, you need the registration code inside that box; there is no activation code via email unless they've opened the box (which they should not do).

I waited for the activation code to arrive on my e-mail

Where did you buy this plan? I am confused with the "waiting for the activation code via email". You buy a box with a booklet inside which contains a page that has the registration number. This is what you then use to register it - unless you bought it directly from Apple in which case you will not get an activation code, but an acknowledgement that you have Applecare activated.

The point is twofold:

First, you not only have to buy the (old) plan within the first year, but you must also activate it within 364 days of purchase; and,

Second, Apple stopped selling the (old) plan some time ago and now only offer the new Applecare + which must be purchased at an Apple store or AASP within 60 days. See here:

AppleCare+ for iMac - Apple

because I had bought it within the first year of warranty.

I believe they made an exception for you; unless they've changed it (and I couldn't find anything regarding that), the rule has always been that you must also register it within the first year. If you bought your Mac AND the Plan from Apple at the same time online, it should have been activated automatically. If you bought the Plan separately later, it wouldn't be automatic - after all, you could have bought it as a gift for a friend who would then want to activate it.

I think Apple should REALLY reconsider the need of sending the Plan physically to their costumers

If you buy the device from Apple along with the APP, then you do not need to do anything as the Plan is automatically activated. It is for purchases later or somewhere other than Apple where you do need to have a code and activate it. And, since there have been many instances of theft (people selling the same code on ebay for instance dozens of times), I would guess sending it in a box is the result of that.

FWIW, if you wish to tell Apple, you would need to contact them - we are all other users here.

Did you get an email receipt from Apple when you bought the plan? That would have the date purchased and would be adequate proof of purchase.

If you used a credit card you can contest the purchase with them and get your money back if necessary.

I'm so sorry! That is frustrating.

The thing is, volunteers not Apple employees respond to discussions here at Apple Support Communities.

We can't help with an activation problem unfortunately,

I hate to say this because of your prior communication with Apple Support but that's what you need to do.

You can contact Apple directly here > Contact - Official Apple Support

or on Twitter: @AppleSupport

*** You might try restarting your Mac then try again

They said they could do it, but the guy there was really nice and polite and promised to try and solve this for me. They asked 24 hours to come with a definite answer.

You get to the right person and you can get some results. Good Luck.

Hi,

Enter the serial number for your device to find out what AppleCare plan you can buy.

Buy an AppleCare plan for your device - Apple Support

Is there an Apple store near you?

Apple Store - Find a Store - Apple

Better to communicate with Apple then wait to see anyone else has the same problem. You might be waiting for awhile 😟

You're welcome. Hope that helps.