I'm currently playing on a level 33 fire wizard and I have progressed so far without Grizzleheim because I never got the level 20 quest from Ambrose. I did the initial quest from the bear in Olde Town with no issues, but when Ambrose called me to his office he had no quest for me. This leaves me with no portal to Grizzleheim and no way to begin questing there even though I am a level 33.
I had an old death wizard who is level 33 and I am able to access Grizzleheim with no issues so it leads me to believe it is an issue with a recent update.
If there is anything I can do to fix it or something I must have missed please let me know.
Ambrose should have sent you on to Grizzleheim when you reached level 20, assuming that you already did the "Bear Market" introduction quest with Baldur Goldpaws.
To get started there, you should first check in with Baldur near the Bazaar, to see if he has anything for you. After you do that (or if you did his quest already), then Ambrose should have summoned you to Grizzleheim starting at level 20. Thereafter, he'll call you back several times.
Starting with Savarstaad Pass (level 20), you'll level up through Vigrid Roughland (level 25), Mirkholm Keep (level 35), Nidavellier (level 40), and then Ravenscar (originally 45, now level 40). After you defeat the Coven in Ravenscar, you'll be invited to Wintertusk. Theoretically, you can start Wintertusk as early as level 40 but I'd suggest waiting until after level 48.
Here's the quest tree that leads up to Wintertusk (and the Wintertusk quest tree is linked at the very bottom of this page I'm linking).
If you're truly sure you did the prequest and Ambrose still isn't giving you a quest, then it might be a bug or glitch. Kingsisle has been having some quest completion glitches lately. You can submit a ticket to support and hopefully they'll get you back on track. There's a link to Support right on the game launcher now, or you can click the "Help?" icon on the upper right corner of this page.
Be sure the email linked to your account is up-to-date, since KI will contact you that way.
Alia Misthaven