The terms of supply (between the supplier business and the customer) don’t refer to the credit limit and the obligation to pay for goods supplied is not limited to that amount.  

Similarly the PPSA provision (to the extent they have registered their interest) is for all amounts owing and does not limit to a credit limit either. So from this perspective credit limit is  not relevant to the amount recoverable directly from the customer – but it would be useful for there to be correspondence between the parties acknowledging the higher level of credit being provided.