I have unlimited data on my plan. A couple few ago it gave me a 2GB data warning and now it's only connecting to 4G, which seems to be really slow and not loading simple apps etc.
I checked my data usage for the month, which is 17GB, but since I'm on unlimited this shouldn't really matter surely?
The data warning is likely to come from a setting on the phone itself (unrelated to the SIM or the service provider).
It sounds like you've set the phone to believe it has an allowance of about 19 GB. You should be able to remove the limit and might be able to specify that connection as unmetered. An online search should show you how to accomplish this.
