500% escalation charge

My 5GB anytime and 15gb night data contract expired on 10 Jan 2016. I was told I cld continue month to month. I was never informed it wld increase frm R165pm to R905pm! I have requested an explanation several times since receiving my acc, to no avail. On 9 Feb I went into Shelly Beach store and cancelled contract. No confirmation has yet been received. As the requisite 20 day notice was given I will block any further debit orders from my bank account. I need feedback and contact details of someone in authority pls.