Have the same problem with my 820 and my wife's 925. Have spent hours on the phone with CC's tech people and gotten several different sets of values to put in the APN settings. After experimenting with them for who knows how long I have managed to get my 820 to be able to send Pictures with Text's using MMS and receive them; but still cannot use cell data to connect to the internet. That should be impossible. The 925 can get on the internet using cell data and receive Pcitures with Text's; but not send them. Neither will connect to 4G lte; but will connect to 4G. Another odd thing, the 820 has a slot for inputing the IP type, the 925 does not. CC's customer support says they have no data for IP type in their data base. Great huh. Those great low costs for service comes at a cost.
I also have a Moto G lte than can send and receive pictures with text's using MMS, and connect to the internet using cell data; but cannot receive 4 Glte. They have no setting for getting 4G lte on the Moto G lte; because the only two Moto G phones they sell cannot receive 4 G lte. Again I experimented with the settings they sent me for their Moto G's but the best I can get is 3G H, right below 4G .