I understand how you feel and I'm not trying to defend the airline but I'll make a couple of points as I'm going to pre-empt what they will tell you when you complain.
The bag is optional. Many people travel without checked baggage and why should they subsidise those who do.
The CC charge on BMI Baby is per booking. LyingAir, or Ryantheft as you call them (I like that!) charge it per segment per passenger. Also (I've not checked on site) but I suspect that if you paid with a debit card, the charge would have been less.
Airport check in - if you can't check in online, that's a scam.
Seat selection. They make it hard, but you can bypass that and therefore not pay for it.
APIS is mandatory and you should not have to pay for that any more than you should have to pay extra for your car engine to have a camshaft in it!
Here's the link to the AUC complaints area :
How to complain | AUC Home
Good luck. Please let us know how you get on.