Vodacom unwilling to help

I signed up for an open contract for R45 per month x 24 months, which gives me 500mb and 500mb night owl data. It turns out i am not on an open contract and Vodacom are unwilling to migrate me to an equivalent open contract, instead they only offering me packages which now cost more then R200 per month. Absolutely terrible now i am stuck with a contract which i cannot use.