That's a shame.  I just tried adding a weeks parking to a booking and they quoted £82.  Surely they cannot have charged you £20 more than they quoted in your booking?

I don't take advantage of Ryanair 'offers' for car hire either as they are never as cheap as dealing direct, neither are the hotels.

I trust them to get me to and from the UK on time and cheaper than any other airline, with the youngest fleet of aircraft, and that's all.  Everything else is their way of trying to make extra money.