https://www.youtube.com/watch?v=LXAwT2njjXs has at 3:34 the final being blown with the bald guy next to the ball and his team mate with dark hair a couple of yards away when the final whistle is blown. If you also look at
https://www.youtube.com/watch?v=KuiRx_NtxbU at 4:22, you can see that before the bald guy gets to be next to the ball and the other guy with dark hair is a couple of yards away, the dark haired guy has already passed it to the bald guy with a small touch of the ball so that shows the corner being taken before the whistle is blown.
If you compare the two videos close enough, it is clear that the corner was taken and clear enough in my view for the results provider to correct their error, it doesn't matter whether this would have a large effect on settled markets or not, if the result has been recorded wrong then it needs to be corrected.
Certainly the first port of call here is to Betradar or whoever provided the result to Bet365 but if they are unhelpful then I personally wouldn't give up there. IBAS and Gambling Commission would generally say that the bookmaker should go by their results provider but if the OP provides this clear evidence that the odds provider has got it wrong, I would say it is still worth taking it to IBAS etc, but first port of call is to Betradar.