email problems

Since Monday 3/8/2015 I have problems sending email messages of size greater than about 500 Kb and/or emails with attachments. I have emailed Telkom support four times since then and sounds of silence are overwhelming. They just ignore me flat. I inform them that I repeatedly get the error message 0x***B or 0x800CCC00F. My setup is that I have a DLINK 2750U modem with a laptop with Windows 8.1 and OUTLOOK 13 and a Desktop with Windows 7 and Outlook 10. Both computers give the problem. This starts on Monday 3/8/2015 without me changing anything on my email settings on the computers. I browsed the internet to get some idea of what to do and all the suggested solutions do not help. I was for more than 40 years in IT with support the main concern and if a user had a problem you attend to it immediately and always follow up. Don't support staff take proud in their work any more. YOU DON'T IGNORE A CUSTOMER ESPECIALY IF HE HELPS PAY YOUR SALARY.