Skaven screaming bell

[Nyeave]

I had my first game ever against skaven the other day and apart from the book basicly s***ing all over every core rule it was a very fun and bloody game.
One question came up however. I managed a multi charge against his screaming bell unit and wiped out all the clanrats and the grey seer on top. However the bell it self was left and for the next 4 rounds of combat i simply couldn't kill it. Apparently T6 and 4++ turned out to be too much for 20 SMs, a silverhelm unit and a noble on griffon...
Now the question is: We ran through the book over and over again and it seems like the bell itself still had a 4+ ward and unbreakable even though the rest was dead. Did we play it right? And if we did, how do you deal with the bell?

[RE.Lee]

The Altar of the Horned Rat rule states that only the Seer and the pushing unit are unbreakable. The errata added the Unbreakable rule to the Bell itself, though. You'll need to destroy it entirely. W6 T6 4+ ward is quite hard to deal with, but a unit of White Lions should be able to chew through it. 24 hits is it?

[f00ssa]

7x3 Swordmasters have 28 attacks, for 21 hits, 7 wounds... with a 4++ save, they alone should still kill it in 2 turns of combat.

After lances the helms contribute little, but the Grifffin something and the Noble maybe, depending on weapon. So if you need 4 rounds of combat, it's more that you need better dice

[Icarion]

in my case, the dragon ate it, twice!
...even the small one with firemage (relic sword, burning sword of rhuin spell plus sunfire gem), but with that one i was lucky with the dices (rolling 11 on the 2d flaming breath hits in close combat), coming from the back while my brave phoenix guard kept the unit from the front. the other time the star dragon used it as chopsticks to eat the rest of the skaven!