SIX MONTHS for statement

In September 2015, I ordered Contact Lenses from Pieter Cornelius Optometrists in Rustenburg. I put the contact lenses on my medical aid, and continued with my life. <br> <br> After the visit, my cellphone number had changed - however, I was not aware that this would be a problem, since they had my email address and work number. Today, on 29 March 2016 - six months later - I received an electronic statement from them, notifying me that I should pay for the statement attached - with added rent because of the payments I had missed. <br> <br> I want to know why they took six months to email me, and why they did not make use of alternative contact methods earlier, when they realized that they were unable to reach me.<br> <br> Although I accepted responsibility for the statement and for not going through my medical aid statements more carefully, I do not accept that they took six months to send me my account.