I was on a Smart 19 plan that came with 500mb data. I wanted to change to a My Flex Prepay to increase the amount of data I got each month. I knew that when I changed plans I would lose the cary over data and minutes I had, which were quite a lot. It seemed worth it. My big isdsue is that I changed plans the day that my old plan had just renewed. I assumed that the change would happen from the next billing cycle. If there were any warnings that the change would happen immediately and I would lose the whole montrh I'd just paid for they were obscure. I certainly didn't see any warnings at all. That really sucks,
Not quite as bad but it was also notg made obvious that as well as losing my rollover data, there were much lower rollover caps on the new plan (3.5GB and 500 minutes). I don't know if there even were limits on the old plan. I had certainly had double those minutes and more data than that before.
Anyway, I can live with the rollover caps but stealing a month of credit without warning is really just plain wrong. That needs to be fixed.