I think that there are a number of factors contributed to the problem. The most disturbing one being the issue of customer service rep lying to customers. I know that it happens in all airlines, and I sometimes wonder whether they use brains anymore in rebooking flights during schedule change, but denying a change of schedule is something else. The whole change itself might not make the OP so stressed, but the attitude of and lies from that customer service reps are big problems.

I always think that those who do not want to be disturbed, or cannot tolerate to be disturbed should not be in the service industry. In this industry, customers are probably the most important sector. No airlines will survive without customers, and yet some customer reps think that they are on top of the world.

Well, I understand that why the OP is being disturbed, but even the best origanization is going to have some ignorant people. I, myself, would give Flyi one more chance at least, to see whether they will do other things right.