ADT security not sticking to our agreement

I installed the alarm at my residential place and when I sign the contract it was 2 years fixed contract n my installment was supposed to be R350 however they debited 1st time in February n the amount was R378 that we didn't agreed on. I called them and I was told in March is going to be less with that R28 as they debited more with R28 in Feb but nothing happened as even in March they still debited more and I called then n explained n call center agent dropped the call for me