Over billing of data usage on account

I been a client of auto page cellular for the last 24 years with the same number , my account always used to be in the region of a 1800.00 per month ,three months ago i received a bill for 12533.21 upon my inquiry I was told that it is for DATA used on my phone, This is not possible as I only receive phone calls on my phone. I asked for a statement where it revealed that from periods *** I used *** kb and this all on a smart phone where the reception is poor as I stay out on a farm. I addressed this matter with my local branch and was told to pay the account before they would investigate it , which is crazy as how can I pay for something I never received or used, This matter has been going on now for three months now with no results and now I have lost a huge contract as the service provider cut my service to phone, This is a company phone registered under Pidi Pidi Construction which I have used for the last 24 years and now I am losing my source of income because of someones incompetence to do their job properly and as a result my business is suffering and losing money daily