Limit on account constantly being removed by Cell C without my consent

I have recently taken out a new contract with Cell C. When I took the contract I asked, while in store for them to set a cap/limit on my account. The assistant assured me he had set one for me. That month, my limit went over. I phoned cell c and the call centre assistant said there was no limit set on my account which is why i have been charged more then my contract fee. She subsequently set a limit and it has been fine since then. The last two/three months, my account has exceeded the contract and I have been charged more again! This is absolutely ridiculous, I shouldn't have to fight to get my account capped every month. I downloaded the app to see what the limit was, It said "no limit". I have no set it myself. Why do you offer this option to cap your account if you are just going to over charge me anyway and negate the limit? It is ridiculous that Cell C can just remove my limit as and when they wish and not inform me just so that i will pay them more money. Its a pity that a debit order goes off my account for this as that "over expenditure" should have never happened in the first place and I should not be liable for it. Clearly cell c just takes the liberty of adjusting peoples limits depending on how much cash they want to make, its really just outright thievery.