APN settings can not be edited/added on unlocked Nokia 2.3.

I've had this phone for about a year and have had intermittent issues with MMS and data usage. It is an unlocked phone. My carrier is Walmart Family Mobile.
Under my APN settings, there is T-Mobile and T-Mobile MMS. I verified with my carrier that they should be set to tracfone.
I am unable to edit the existing APN settings, and whenever I add a new one with the correct information and click "Save" it takes me back to the previous screen with no new APNs to choose from. I have power cycled a hundred times, reset all my APN and network settings, used third-party APN apps (that bring me to the correct screen but with all options to edit greyed out still), updated my APN through my carriers website at which point I received a text saying "We are sending your phone an update." but after an hour and multiple restarts I still only have the T-Mobile options. I've done everything I can think of to try and fix it. My carrier said there's nothing they can do about it since it won't let me add a new APN. Is there anything I can do? This has been such a hellishly annoying issue.
The thing is, it works occasionally. I'll get a flood of backed up MMS messages from the last few days, and then I can no longer send or receive them. I imagine that has to be because Wal-Mart Family Mobile uses T-Mobile's towers, but I don't know. It's not a T-Mobile SIM card, it's the one I was sent when I signed up for the plan. And like I said, it is definitely an unlocked phone. I don't understand why T-Mobile has any business forcing their APNs onto my phone. Am I SOL or is there something I can do to force my phone to accept my carriers network information?
By default, my network is set to HOME. Occasionally, when I open my network settings, it shows my network as Family Mobile and then immediately switches back to HOME. When trying to select a network manually, HOME is the only option available.
Help please?