Telkom pushing for upgrades on ongoing contracts

Telkom contacted me via sms to let me know that I am due for an upgrade, afterwards I was contacted several times to upgrade, eventually I did upgrade. Now I am liable for an amount to pay on my old device because I was not due for upgrade yet, their sales department seems to just have been pushing for sales. Make sure you are due for an upgrade and that there is no outstanding amounts on your old device before you upgrade, because they are unwilling to assist even though they did not inform me that I was due to pay more, I made the inquiry after I saw the huge amount that went off on my account.