This,
Any issues I've had with sensors I've contacted Abbot (Libre) direct on their customer helpline. The first call was a bit of faff as they must have gone through all my details at least 3 times, but after that it has been fairly straightforward.
The issue with going back to the GP/pharmacy, in my Health Board area at least, is that you only issued a certain number of sensors per year. No matter what the issue or reason is for wanting extra, if you go over the magic number they will refuse to prescribe any more, so going directly to Abbott and having them send out replacement sensors circumvents any issues with your GP.