Any idea why BA telesales cannot price a WT+ fare to NYC, originating in AMS or BUD or LIS?

I get the fare using ITA, also on expedia, even on ba.com. The problem is I want to do an open-jaw (can't do on ba.com) and I want to MFU it (so has to be done through ba).

On the phone, BA tell me there is no such thing as a WT+ fare ex-EUR (as there is no WT+ cabin) and they insist it can only be priced as 2 separate itineraries, which doubles the fare.

They can't even price a simple AMS-NYC return for less than double the online fare? I have told them to use T and Y classes and given the fare basis TLRCEUR, but they say the computer won't accept it. Have tried 3 different agents and got the same thing each time.

Is it possible the online fares as "not for the UK" fares, and therefore not available from BA telesales? Or are they doing something wrong?