2Talk - not connecting to international calls to SA

I have 2Talk via HG659 modem, on UFB. Linksys SPA2102 and panasonic cordless dect.

It works fine for national calls and internationally calls to other countries. However, recently it has not been connecting to calls in SA. I get a dial tone, and the phone rings on our end. however, folks in SA have said (after we checked with them) that their landlines do not ring on there end. Or they answer, and dont hear anything at all.

We can also get incoming calls just fine from national and international callers (including SA callers).

2talk investigated a few days back and the problem seemed to fix itself, and now has reoccured. SAP2101 is 2talk supplied and provisioned.

Thanks guys