Samsung Galaxy s4 is lagging big time with messages but calls are just fine, Help?!

Okay, so about a month ago i activated my at&t samsung galaxy s4 version 4.4.2 with metropcs. I was so excited because i was in much need for an upgrade. It was working just fine until two days ago. My messages take 1-9 hours to send and also to receive. I can make and receive call just fine. Ive searched all over the web but noone has given me the right answer. Ive restarted my phone, taken out my SIM card and checked my wifi, and even went to my local metropcs store to see if they could fix it, it worked for a couple minutes and i thought it was fixed, but im still having the same problems. Idk if its my carriee or my internet but it s really frustrating me. If anybody could please help me fix this problem i would really appreciate it, thank you.

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