wait... You didn't actually reach the gate with bags the size and weight of the 23kg type now, did you? If your carry-on was 9kg or heavier (the limit being 8kg) then they were within their rights to charge you (and indeed they charge ridiculous amounts for each additional kg), but what I didn't get is if you had already exceeded your checked bags allowance or not (did you already have 2 checked bags on your name/ticket?).
You could have tried to fit 1-2 of the heavier objects in the "personal item" in order to be under the 8kg limit though.
Or was it actually at the check-in desk and with regards to the 23kg bags?