*shrug* you turned up with 30Kg over the allowance and was charged excess fees. EUR50 per Kg doesnt sound that abnormal. That you travel on other airlines with large amounts of luggage is irrelevent

BA and AA use the piece based system for luggage allowance and permit 3x32Kg for 1st class ; EK permits 50Kg total; different airlines, different rules

If over the limit, what really is there to negotiate; the rates are set ; you had a choice of paying, discarding or arranging the excess amount to be shipped in another manner

I am currently travelling for 2 months and have just under 21Kg

You could have paid for the excess luggage at a discounted rate (20% discount) online in manage your booking and got it down to EUR1200