Interesting to see the "too little too late" comments on their comments. Proof that 1) no matter how hard you try to apologize and make things right, you can't please everybody and 2) unfortunately, these people are the most vocal.
So the customers spent hours comparing the offers of the competition, all the time being frustrated because this jumped on them from nowhere. And then, 2 days later, they hear "Whoops, my bad!". That just doesn't fix the damage, now does it?
If a thousand customers each spend 3 hours worrying about what to do, and these numbers are conservative, then you've created 3000 hours of unnecessary frustration. So the damage will exceed $300.000. Just with one ill considered move!
Whoops, sorry!
I guess most do a analysis when signing up and would either forget about it until they hear of something cheaper from somebody or do a reevaluation after a fixed period of time like say every 3-6 months.
This sudden price change made everybody stop what they were doing and look for an alternative now. And people spent time doing research, brainstorming alternate ideas and some made the switch already and now they say Oops!. This is why they are griping.