I'll give it a stab, since in two years you still have this problem...
First, make sure you CANCEL any other pets you have cast (Deity pets, Necro, Conj, Illy, even Defiler). Next, use your Phyns ability to recast your 'invisible' pet.
1- Look in your maintained spells. Do you see the icon there that says you have the pet cast?
2- If yes, then try '/pet_options' ...that should bring up the pet options window (naming, follow stay etc). Click the large button that hides your pet off and on until its visible.
3- ??
4- Profit.
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Things I sometimes play...
"What do you want to be when you grow up?"
"I want to be a unicorn!"
"Awww, why's that?"........
"So I can stab people with my face."