Wrong billing

On the 1st of November 2017 I went to vodacom 4u to apply for a data contract of 10gb day + 10gb night at the promotional price of R249, it was approved but later that month an invoice came in billing R299 + CLIP I then went back to the store to complain about this and the gentleman assisted in migrating me to a 20gb day + 20gb night as it was going at R299. The issue arose when This month's bill came at R808 which forced me to go back to the store to quiry this but since the 3rd of Januay 2018 I have been fighting a losing battle with no solution, this is a problem now because I am 5 days away from the debit date and I will not afford the proposed invoice. I am pleading vodacom to sort this out