Telkom Users Beware !!!!

To all Telkom users . I have 2 domains at Telkom and since the beginning of the year ive been experiencing problems with e-mails disapearing into thin air ! I kept contacting Telkom Call centre ,they test my domain's and e-mails and says nothing is wrong !!! The times when i had the energy to push hard enough they would say they will esculate the problem but absolutely nothing happens !!! ....Out of desperation i went onto the Telkom website , Logged in with my modem username and created a e-mail (alias) 'my streetname' @telkomsa.net in order to receive e-mails and what happens ? Suddenly i am receiving someones personal statements and facebook notifications ..... I soon realised this e-mail address actually belongs to someone !!! My question is , How is it possible that i could create a alias e-mail that actually belongs to someone else and now i receive his or her e-mails ? How secure is Telkom actually ? What happened to all my business e-mails that dissapeared ?