Mtn south africa Facebook misleads winners

Hi Hello Peter I entered an Mtn competition via Facebook for checkers grocery vouchers, the sms stated 500 X 12 months ,every month I will be sent a new voucher worth 500 for the remaining 11 months I only received one X 500 for the month of October, they are misleading the winners with false information which says 12 X 500 voucher per month, there are a lot of complaints about MTN and I feel someone working in the prize department is probably using those vouchers please assist also won airtime which I have been nagging about I gave up.please assist