Intimation u/s 143(1) - ITR3

Already checked everything. AY is correct in ITR, challan, everywhere. 

The only option for me is to submit a disagreement and my only confusion is between 

1 Demand paid and challan has CIN (without open challan details) 

2 Demand paid and challan has CIN (with open challan details)

That is, with or without open challan. Which to choose?

Actually both are same - demand paid and challan has CIN. Difference is "with open challan" and "without open challan". What is "open challan"?

I think you need to file rectification for the same. As regards new portal, I am facing the same problem of not finding link for filing rectification. If you check intimation, it says after login to new portal, go to services tab where you will find rectification link. However, I couldn't find the same as well.

You are correct. I called CPC and they say they have no idea when the rectification link will become available. This is just a hassle for common people. Send wrong demand and then don't provide the link for reprocessing.