Default MMS download unsuccessful

The general problem that I'm having is that MMS messages won't download with the error message: Download of message... was unsuccessful.

Here's some background:

I am using Straight Talk. When I first ported my number over, I had a Verizon Samsung Galaxy Proclaim (CDMA). I used that phone for over a year with no problems downloading MMS messages. Then, I ported my number to a Verizon Samsung Galaxy S3 (micro SIM - GSM using AT&T network) and didn't have any problems with that phone downloading MMS messages either. I broke the screen of that phone and ported my number back over to the Proclaim, but I can't remember if I was able to download MMS messages or not. Then, I bought a Sprint Samsung Galaxy S3 off of ebay that was flashed with a Verizon MEID. I am not sure what that really means or what type of files were used to flash that phone. I can probably get that information from the seller if needed. Anyways, when I tried to use the last phone, I lost MMS downloading capability. I can send MMS messages fine. I can also receive them, but I cannot download them. In attempt to save the sale, the seller then flashed my number onto another Sprint Samsung Galaxy S3 and that phone also didn't have MMS downloading capability. So, I ported my number back from the second Sprint Samsung Galaxy S3 to my Proclaim. After all of that, I have now lost the ability to download MMS messages on this phone which has always worked for me.

I have read a ton of forums and done everything I can to troubleshoot. I have unchecked "auto-retrieve". I have wiped my phone and SD card, but nothing is working. I have an escalated ticket in with Straight Talk, but in dealing with them in the past, I have little faith that they will be able to fix the problem. From what I have read, the problem I am running into seems to be Sprint related.

Any insight would be greatly appreciated.