Trying to buy extra fly tickets. According to the every mathematical rule 160+440= 600 but TK says it is 870...

No explanation, no warning nothing. I realized the last minute that it was super high and called the CS and he says oh tickets are too close, system increases automatically. This is illegal in my country I live so let's see what consumer board will say to this...

PS: Same flight is on codeshare sale on Finnair and guess what? It is 608 Euro same category.