Yes you don't need to 'prove' anything, all I'm saying is, if the guy doesn't understand what you mean by duplicates, explain him...
Also if you make a charge on one it comes up on all,
That was my push to call them, as they reported a lot of spend even though was very little, and yes if you have a lot of total available credit is also good, but not if you use even 25%...
Now there is an advantage in having them, is if you want your average age high, give it a few years and it will be hard to lower, as you have a lot of 'old' cards,
But aside from that, I see no benefit in leaving them on