Bad service ever!!!!!!!!!!

I bought i phone in September 2017 the payment agreement is R269 for 24 months. End of October i paid around 500.00 whic i understood due to the fact that i was paying for the few days of September. In October again i paid around R600.00 which didn't make sense for me. I called the call center i told me that is a speeding limit, i immediately canceled the spending limit. Again end of November i still paid more than want i expected even though I canceled the spending limit. December i paid R852 i went to the store to complain the said the spending limit is on my phone not on the contract. We changed the spending limit R1. 00 but end of January i they debited R852. 00 again. So i don't know what to do now. Please assist me someone.