Advance me voucher

I took an advance me voucher with vodacom in February for steers then where I live they do not accept vouchers(steers Jubilee) then I decided I wouldn't pay for something I couldn't use then I called vodacom to cancel the voucher for me of which they promised they did. After some days I started receiving sms that vodacom couldn't charge my card then I logged the second call and again they promised that they did cancel the voucher but again I received another sms last week stating that they couldn't charge my card then today I call vodacom only for the agent to drop the call on my ears