Stop leveling anyone else, and get Bellower to 60. He is far and away the best campaign farmer you have. Don't waste any more time leveling Elhain, you don't need her since you have Bellower.

So long story short ignore everyone else in the forum and level up bellower instead of Elhain?

You'll  still  use  Elhain  as  Arena  nuker  and  dungeon  damage-  just  focus  on  Bellower  as  Campaign  farmer  to  help  speed  up  your  progression.

(And  by  the  way,  you  can  save  yourself  all  those  photos  by  clicking  the  full-screen  in  top-left.)

That is a debatable recommendation... yes, Bellower is a faster campaign farmer than Elhain, but she'll get the job done in a reasonable time too and she'll do a lot more in arena. In dungeons it kinda depends, both can play a significant role. It may make sense to make Bellower your first 6* champion if you want faster farming, but unless you pull some game-changing champion in the meantime, you'll probably still want to take Elhain to 6* as well. 

After those two, your best champion is probably Melga, also a future 6*. 

To be fair, I never farm campaign, only battle for dailies/stars. I have advanced much more in dungeons/keeps, and farm keeps (once for force/arcane and twice on spirit/magic) and ice golem(most progress in auto) for silver and xp every week. 

Probably that's the reason why you have no lvl 60 champ so far. Campaign gives so much more xp than dungeons, do yourself a favour and start levelling food champs in campaign. It doesn't matter if Elhain or Bellower does the job, just get it done.

If you can't do 12-3 brutal with 3 food champs, do 12-3 hard until your campaign farmer is able to do 12-3 brutal alone.

why 12-3 and not 12-6? If I need 60 champ so bad, I should aim for xp

The  XP  is  not  that  huge  in  difference  in  12-6.  Usually  it  is  better  to  farm  12-3  and  "double  dip",  still  getting  good  XP  but  also  building  up  silver.

even with an xp boost in play, 12-6 only nets you an extra 150 xp per run. while it is the most efficient option in terms of xp (outside of nightmare, which isn't a viable option for you atm), it's a fairly negligible gain. over time, it will start to add up but so will the cost; you lose roughly 550 silver on a common 3 star piece of gear, with the gap widening for each additional star or rarity. overall it's a pretty poor tradeoff.

In addition to the above said, 12-3 is very easy for your starter champ, as 11 enemies have spirit affinity and only one in the first wave force. 12-6 has much more force affinity and will take longer for your Elhain.

I am stuck on 11-7 :(

Then you might want to farm somewhere where you get a 100% win rate... 

U are getting there!

you can either use the best stage you can grind on until elhain is ranked up (probably 10-3, but you might be able to do 11-6), or you can bring melga up to rank 5, which should let you clear 11-7.