If you’re planning to stick this out your top priority should be to get the email implying the rate may be honoured. With that it should be possible to argue the case for a chargeback on the basis of what you were told if the Avios are not paid out. The deal overall includes an incentive, and you have queried the incentive with the reply containing an implication it will be honoured, even if it’s ambiguous.

it’s still a gamble but there’s a higher probability of success I’d say and a possible off ramp after the return window. Personally I’d already be out for reasons explained upthread, but that email seems very encouraging.