soft lock activated but billed

Why do cellphone providers have a soft lock if it is never implemented. I put a cap on my account and received confirmation on 2 March. To my dismay, the bill was run up without any notification that it was an open line. I have the store fighting the battle for me and they have been nothing but helpful but the people setting up accounts and the billing departments need to explain to me how i ran up a R4000 bill!