Hi all. Hoping one of the FT gurus can help me out with this one before I spend (potentially) a very long time on the phone to UA.
I'm trying to book a one way ticket IAH-DXB on September 16. The flight I want is either one of the following:

• IAH-LHR-FRA-DXB (UA880 - LH901 - LH630
• IAH-FRA-DXB (UA46 - LH630)

Searching these flights one way IAH-DXB shows M as the lowest fare class available and prices it out at something like $1,300. However, searching as a multi-city IAH-FRA then FRA-DXB prices out in W at around $620 which is far more reasonable. The problem is the flights aren't actually bookable and it tells me to call in. Even more frustrating is that both days either side price out around $600 one way IAH-DXB for the flights I want, but I would really prefer to travel on the 16th.

Does anyone know what is going on here? And whether I am likely to be able to get this booked if I call UA? or am I just wasting my time. Thank you!