MY AIRTIME LIMIT IS UNLIMITED I DONT KNOW WHY!!

I had my phone for more than a year now ***) I have never been billed so much that's why I took a second phone***). <br> After I took my first phone they called me and asked me If I was happy I told them yes and if they can stop my airtime after I have reach my limit , this has not happened. Now I am told that I owe R3118.11 from December , January and February , why o one told me about this ? I cant go and get a bank statement everymonth to check I am billed correctly because I have never had problems with you before. How I am going to afford to pay so much money ? I want this to stop now <br> <br> I wanted to upgrade my phone but after this no thank you, you just lost a customer in me .