Telkom making money by increasing limit

I took up a Smart plan 100 mobile contract in September 2014 which allows 1g of data per month and an additional 100 free minutes @ R399 per month. Once utilised, it then becomes similar to a pre-paid device which requires airtime to be purchased. I was clear from inception that I did not want any limit set. I received my bill earlier this week only to find an amount of R666 charged. The additional R267 charged is in respect of voice charges. I immediately queried this with the billing department who were nothing but useless. I eventually got through to a manager Sibongile who then confirmed Telkom had a promotion running in June 2015 which automatically increased my spend limit to R500 per month, without my consent or request. She then confirmed that this was a bulk sms function that was sent to customers and couldn't confirm that this was sent to me as notice. I have never had the need to top up on this package since inception as I have an alternate contract with another service provider that is unlimited for both calls/data services. It seems like Telkom just increased the spend limit without my permission all in an effort to make some money. This has been happening since July.