Caught out by Ryanair?

I have flown with Ryanair many times with no problems, but I was caught out by their new baggage policy. When it came to choosing the type of ticket I wanted I saw three options: the first was the basic ticket which allows only one small bag; the second was over twice the price but allowed priority seating and two bags, one small, one large; the third was a bit dearer than the second and was described as 'flexible' (I think). I'd read about Ryanair's new policy and knew that I'd have to pay extra and that priority seating was more or less compulsory, even though I didn't need it, but I did need to take a bigger bag, so I chose the second option. Then I saw that priority seating and two bags should only cost €6 to €10 extra. When I asked why I'd paid nearly €40 extra, I was told I should have chosen the first option, then added priority and two bags to that. I saw nothing that told me I could add anything to the basic ticket. My ticket gives me a 20 kg check-in baggage allowance, but I don't need that. The only bright side I can look on is that I've only booked the homeward flight and I can get the right ticket for the outward flight.