Ridiculous Data Charges

On 13 April 2015 late afternoon I went to upgrade my phone at Vodacom shop in Village Mall, Hartbee****rt. The gentleman who assisted me informed me that he will do all software updates in store via Wi-fi as I was worried about data charges until they activate a data bundle. After doing the software updates I was sent to another shop in the mall to cut the sim card as it was too big for my new phone? I went home afterwards and on 14 April got a message that my data bundle was depleted. I phoned my son in law who advised me to switch off the phone until I can query the high data usage on my phone. I went back to the same Vodacom branch and was shocked to find out that my data bill was already over R1800-00 and this is for data supposedly used between 17h30 on the 13th until 10h45 on the 14th. All updates were completed in store via Wi-fi? I did not even use the internet during this period??? All attempts to have the amount revoked have been in vain.. Please help as I am already in financial difficulty and I can really not afford this!!! I have been a loyal customer of Vodacom for many years and never had any issues.