I've been flying OAK-OSL for the last 5 years and this is the first time my carry-on was checked for weight. I was charged $80+ at the gate in OSL (yes they have a credit card reader at the gate) because my "carry-on + personal bag" were 1kg over the 10kg limit. There was no time for me to open my carry-on to sort & discard unneeded items because they opened the gate too late, and everyone was in a hurry.
When I gave them my carry-on so that they could check it in, the agent said no, and to just take it with me in the cabin. ...? Can I file a dispute with my credit card?

* I saw people throwing away chocolates and stuff that they bought at the duty-free shop because of this. I think it's unfair that they don't weight them at the counter, so that it gives passengers more time to discard items, or to warn them not to buy more heavy items like chocolates after security checkpoint.