Trouble adding new companions

[SexualMoth]

Hello, like the title says, I can't seem to add any new companions, and I've had this problem for about a week now. When I buy a pet cage and right click it, a message written in red pops up on my screen, saying: ''Can't add companion to your account'' and nothing happens, the cage is still in my bags. I'm not ''capped'' with pets, I have 1/3 of one pet that I can't add and 0/3 of another.

[DbaPM]

There is pet cap you can get is 501.

[SexualMoth]

That's it! Thanks!