Cunard conundrum

We are booked Cape Town to S’ton on QV, transfer to QM2 for S’ton to NYC sector. Now that QM2 is calling at CT, any advice please on how we change to an all QM2 voyage, CT-NYC. Surely this request to transfer is not a big deal, as when we booked, this option was not available. Seems TA is dithering - waiting on Cunard. Meantime Cunard are advertising incredibly well priced fares CT-S’ton/NYC on QM2.