Looking at the fare rules on Expertflyer, there are 184 permitted routings explicitly published.

I won't copy them all here but will happily PM to the OP if desired. Maybe the OP's particular requirement didn't match any of these ?

It's still not clear to me how the OP booked the ticket, who denied the desired routing and how the eventual routing was arrived at. All done through BA or a TA ?

hth