Cacann,
You may need to add MMS APN settings. For some reason mine were wiped by the 8.1 update and my network profile won't update. You may have the same issue. My phone started working again after I followed the instructions from this thread elsewhere on this forum titled "Cannot receive MMS". I can't post a link, but the pertinent part (provided by Lindsay Brunetto) is copied below:
I'm on at&t with a Lumia 1020 & I had to add back in my apn settings for MMS under Settings > Cellular + Sim > Sim > edit MMS APN. After I did that my mms's have been working ever since. This is what I used (only included fields which need text typed into them):
APN: pta
WAP gateway (URL): proxy.mobile.att.net
WAP gateway port: 80
MMSC (URL) h ttp://mmsc.mobile.att.net
MMSC port: 80
Note this is after I upgraded to 8.1.
08-21-2014 12:52 PM