No notification, couldn’t add more data once out

I knew I was running low on data but I was expecting to get a notification. I did not receive any notification even though I have the notifications turned on and then all of my data quit working. Once I realized my phone wasn’t working properly because I was out of data, I tried to access both the Lum app and the Lum website and I couldn’t get onto either so I couldn’t top up my data. I was only in cellular coverage and did not have Wi-Fi. I should still be able to access the Lum sites even though I was out of data. Once I was able to get back into a Wi-Fi area I was able to add data and then everything worked fine.