I was under the impression that on each anniversary of our accounts, we get some kind of gift and/or a pet slot. Is this the case and where do I find it?

It should be triggered by visiting your Dashboard. On your first anniversary you win a Gold Account Medal, and on the following years a Loyalty Box.

[Edit] You can choose one option of a few from the LB, an extra pet slot being one of them. I took a half-assed screenshot of the options given.

You don't get a Loyalty Box for your one-year, only at two years and up.

Oh well, nice while it lasted. Now I just have to work if I want to pay for the extra slot lol.

Thanks again for answering though!