Telkom problems

A colleague of mine has Telkom as his Internet provider and his email address is @telkomsa.net however for the last month he receives emails but cannot send emails. He has been to Telkom at Cresta and Clearwater at least 8 times to get it resolved. When in the Telkom offices he can send emails, but as soon as he is anywhere else it will not send them. His modem has a Telkom SIM card. We called Telkom yesterday and were helped and able to send emails, but today, its back to them not being sent. This is pathetic and needs urgent resolution.