Automatic allocation of spending limit

I took a 24 month Contract with Telkom on June 2018 for 40 Gig data which i was pay R269 monthly. I will be allocated 40 Gig data monthly and when its depleted i will not have additional data. Then if i need more data i will be expected to buy to topup the depleted but not even once did i topup the data because i was surviving without additional n will wait for the new month to get my allocation. After 12 months to be specific in July 2019 telkom decided on their own without consulting me to allocate me R500 spending limit. Then i continue using my data normal like i used to.My account was now R769 n i tried calling them to enquire about my statement and could not get a respose then in August i went to the Telkom shop to enquire about the balance and that when i was inform about this spending limit which has also affected the month of August whereby i must also pay another R769 which now amounting to R1538.. I lodge a complain with ref no:***2 which i was informed that a contract comes with the spending limit of R500 or R1500 n they cannot credit data that i already used. The Question is Why was i not allocated the spending limit since the inception of the contract, Why was it allocated now after 12 months, Who authorise the allocation n Why was i not informed about it so that i can be responsible when using my data..I took a R269 per month contract based on my affordability i cannot be forced to a limit without my consent which i cannot afford I took a Contract of R269 per month based on affordability rate