Just call for a replacement, they will tell you if you are calling too much. But if it just reads lo they will have to replace it whether they want to or not. They might want it returned though, but they will send an envelope for that. If one of the reps ever is not nice or cooperative, keep track of their name and if they ever answer again hang up and try to get someone else. Most of them are very nice, but I have run into a few in the past that haven't been.
You can get a Miao Miao to attach to it and use tomato ap, xdrip etc to calibrate it for more accuracy. Which one kind of depends which phone you have. They are not as nice as a Dexcom, but they are cheaper, especially in the US. I have worn both and the Libre is great to have, but the Dexcom is better.