****mers using MWEB

For the second time I have had an email intercepted by a third party. The email was containing an invoice which needed to be paid. The person who intercepted the email changed the banking details. The first time it happened I got ****med for R22,000 but eventually got it back. This second time it was for R24,000 but luckily I checked with the other party as to what their account details were and luckily discovered that they were with a different bank to the one on the email. When it happened the first time I went to MWEB in N1 City but they had moved, the security guard told me they were now in Canal Walk so I drove all the way to Canal Walk but they do not have an office there. I have tried to contact them by email but get no response as I want to know how someone can intercept an mweb.co.za email, also they seem to be nowhere to be found in Cape Town. I am reluctant to change my email address as it is such a faff and I also have my wifi account with them. Any suggestions anybody?