Disconneting line usage

For the last two month after payment has been received by Vodacom the usage of the line is being cut. Yesterday we phoned 9 times before they unlocked the account. This morning the account has been locked again. So this morning the call center explained that we have reached the credit limit over a period of two years. When we took out the contract no where it was explained that their is a certain credit limit over a period of two years. Taking out a contract with Vodacom a package is given to you according to your affordability. After the initial contract was taken out a consultant phoned explaining that there is a high data usage on the phone and if we will be interested rather to change the contract package which will suite our needs better. We agreed to the change of this package but now we have reached the credit limit. We paying monthly installments on a Vodacom line that we cannot use. And no where once was it explained that their is a credit limit over the two years. So in our view we are giving money to Vodacom for free.