Your own email address gives a 'address cannot be found' message

I am trying to send urgent messages to your *** address and they keep on being rejected as 'no such address', despite the fact that I have received message from you at that address today ! I am going overseas and need my medication urgently. Please dont ask me to ring your 0860 number because my cell doesnt do those numbers. I dont know why you dont just also advertise your 011 numbers ! Please advise what is wrong with your emails.