I, too, just last month experienced the same thing. I called in a refill of my Colazal prescription and went by the next day to get it. The girl at the pharmacy window said, "That'll be $284." WHAT?!?!? I said, "No, it should be $25." And we went back and forth until she finally said that there was a generic now for Colazal and that is the only one my insurance would cover.
In fact, just that same week, I'd received a letter from my insurance company saying they would no longer cover my Rx for Nexium; I'd have to get the generic. GRRRRRRRRRR!!!! I don't know WHY they didn't tell me the same thing was going to happen with the Colazal.
So I had to leave the pharmacy without my Colazal and call my GI to find out if HE thought it was OK for me to take the generic. His nurse said he said it'd be fine. So back I went to the pharmacy to have them fill the BALASIZIDE...or whatever you call the generic of Colazal. OMG, I HATE not being able to pronounce a drug that I'm taking! 
Of course, so long as the generic works, I won't complain as now I'm only paying $10! But still, it's the principal of the thing. I feel like I'm being given the lesser version of the medication I need.
It is true, though, that if your GI thinks the generic is not good enough for your situation, he can call your insurance company and tell them to cover the Colazal.