Unfortunately, that doesn't seem to be working for me. If it doesn't get upgraded mid next week I'll try cancelling and resubmitting. Do you recommend waiting a certain time before resubmitting after cancelling or just do it straight way?
You should be able to cancel and then re-submit a few minutes later.
The last time this happened to me (I requested a points upgrade on a domestic flight but it was put in a waitlist, even though there was U availability) it was because the booking hadn't been ticketed yet. Once I realised this, and the booking had been ticketed, I canceled and redid the request and it was confirmed straight away.