You bought a MINI-pet? You don't summon it. Move your mouse over it and it should pop up a message saying "double click to take out or put away" (or something to that effect).
See:
http://wiki.guildwars.com/wiki/Minipets
EDIT:
I'm not much of a PvP-er. From the wiki: "All of them can be unlocked
by paying with Balthazar Faction or Zaishen Coins, or only the non-prestige ones by purchasing the Pet Unlock Pack. PvP characters can only get a new pet by charming one unlocked in the Zaishen Menagerie."
You learn something new every day.
