2nd charge off

Collection agency claims that they did not buy the loan from Wells Fargo but are merely acting as a 3rd party trying to collect for them? Doesn't an institution as big as WF have their own internal collections?? Anyway, w/no risk of foreclosure from 1st after FINALLY getting mod we're wondering exactly what is going on concerning the 2nd? The c/a is threatening "legal action" but if they are truly only acting on WF's behalf what can they really do? I thought that if WF still holds the interest in the home as their security they could only foreclose or attach a lien. I thought that the c/a could only seek a judgement against us if they now owned the loan. Wouldn't that then mean that it is now unsecured? But if WF still owns it isn't it still secured?