My Chase Visa CL isn't in your league, but I had a similar experience.   I was pretty pi$$ed too, they cut my whopping $800 CL to $300, so I called the backdoor # once I was sufficiently in control.  I was very nice and amazingly so was the Rep I spoke with.  She "softed" my report and reinstated my CL to $800, no problem.   She further explained the decrease was a "computer generated" deal, and that it may happen again, and that I'd just have to call again to request reinstatement.   I was also told that I was welcome to request an actual increase, but that would definitely require a "hard" pull.  I'm waiting for some further improvement and some inquiries to drop of before I do that....not sure which report they will pull.