Default SMS Troubles - Can Send but Cannot Receive

Hi all. I am not on AT&T so I apologize for posting here but I wasnt sure where else to seek help. Hopefully someone may have an idea.

I recently got a phone on the Pelephone network in Israel. It is a Galaxy S3.

I am able to send SMS texts with no problem. I am also able to receive texts from other phones in Israel no problem.

For the first day or two everything went OK but then suddenly I stopped receiving texts from my friends in the US. They receive mine, but I cannot receive theirs.

My company tried diagnosing this with carrier. They insist everything should work. All the right plans are activated, etc. They even swapped out the SIM. After that the SMS worked fine again for about a day, and then, like last time, stopped working...so people in the US can still receive mine, but I cannot receive their replies anymore.

They are replying in the same way as in the past (replying to my text) so it did work...it just stopped.

I have tried a factory reset which didnt help.

Any ideas?