unlocked S6 Edge will not accept SIM card from foreign carrier while travelling

ihatemysamsung

    I have an unlocked S6 Edge that was able to work on a carrier in Canada in January and now for some reason will not recognize the SIM card i have for the carrier that I use when there.  I first had this problem in South America last  month, on my return to the USA my T-mobile SIM worked fine, then upon return to Canada my phone gives an Invalid SIM card message

     

    I went into the local dealer where they issued a new card to no avail - the clerk took said new SIM card and tried it in her phone and it was fully functional.   y next step was to do a complete factory reset   I still have no service

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