Default MMS not working...

I've been trying to setup the phone to send and receive MMS's without success until now.

I've tried to use the default APN's, I have edited the APN's to the correct ones, I have switched the SIM cards, etc.. etc... and no success... Everytime I send an MMS it just says: "Sending...", "Resending...", "Failed...".. When I receive an MMS, its the same, the downloading always fails.

I have 2 Oppo's R819 in my home, and both have the same problem.. The SIM cards I'me using have no problems with MMS's on other phones, I just cand send or receive on my new Oppo R819...

Can anyone help me to solve this?