You are not alone! I went through almost this exact thing a few months back. I pumped, and pumped for about 7 months (exclusively), and then I realized that all the milk I had (I calculated something like 2700 oz.) seemed bad! I have some news for you though: I'm willing to bet it's not actually spoiled. It is quite hard to find info on this, nobody I spoke to seemed to know what had happened--there were tons of suggestions that maybe my freezer had shut off, and everything had defrosted and then froze again, and suggestions of the like. Here's what it is. It's an excess of an enzyme in breastmilk (the enzyme is called Lipase), that keeps the milk sweet and overall tasting good. There's no evidence that it will harm baby if it's drunk, however most babies won't like the almost soapy taste. I can't post any links for you unfortunately, but if you look it up on the net, you should be able to find more regarding this issue. The truth is that it happens to many women! My sister, and SIL also had the same issue and my sil was devastated to find out that her frozen supply was bad as well. She even asked a nurse about this, and the nurse had no idea what she was talking about.
I'm so sorry to hear about your situation--it is just heartbreaking to throw all that milk away. Someone told me though that some hospitals MAY take your frozen milk with the excess lipase in it to give to preemies, since it is still very beneficial to them. So if you just can't bear to throw it in the garbage (which is what I ultimately ended up doing), maybe give a hospital in your area a call and see what they say? Just a suggestion

Also, there is something you can do about this if you are still able to pump your milk, so it doesn't go "bad" so fast (basically it begins to go "bad" as soon as it is expressed). You can scald the milk right after it's expressed, on the stove in a saucepan. I think it takes some technique to it, and it has to be done just right as to not destroy any of the antibodies (otherwise, you might as well just formula feed!), so if you're interested, try looking it up as well.
I hope this was of some help to you! It took me a long time to find the information, so now I pass it on to anyone who pumps and freezes. Again I'm so sorry for the loss!
Whiskers