Billing query, total incompetence & unprofessional

Average usage for two data ipad deals varies between R600-R1600.Includes 2GB free data per ipad (Cell C).The 2nd anniversary of the contract (28 Feb)I received a surprise bill of R5882 for out of data usage.I then disputed this with the call centre.I spoke to Mlugisi, Mogadi and Daniel & was given the Ref.no. 594402.I requested the itemised billing url's.I also queried what contact details were present on my profile.They gave me bogus contact details & information on my profile as listed on the their database.I corrected this info only to phone back later to query the change & to find no changes made.They eventually sent me just an account proforma with my name & the data used with the cost.Still no itemised billing.I then reversed the debit order and awaited their contact.I was then contacted by the call centre on the 24 Mar & queried with when I intended to make payment. She advised me to send a signed letter to request the itemised billing. I comp**** with this. On the 13th April a debit of R9551 from NU DEBT Auto was made. I went to HQ today & they have no records of my correspondence.TOTAL incompetence.It is ******* to share my details with a third party debt collector! HELP!!