Unacceptable Conduct

I opened a box at PostNet Kyalami in March 2019, the subscription was for 12 months at R700, strangely during November 2019, I receive an email stating that I need to pay a renewal fee of R700 failing which my box will be closed. Now I then enquired as to how that is possible as my 12 months have not yet elapsed. I was basically told that that is how they operate. I then enquired as to why this was not explained to me when I specifically paid for a 12 month subscription and signed a 12 month contract at the beginning of my contract. Only thing I was told was that that must have been an error on their part. The owner of the store does not respond to emails or calls. I have basically been ****** of 4 months of the remainder of my contract. I have received no assistance from PostNet thus far.