Bad service

I'm on a top up ********** 983 contract, I get 1gig & 1gig free after midnight. Since from inception I've been paying R75 monthly cos I don't have Insurance. My November invoice says I have to pay R167 & already my December bill is R425.13. How did Vodacom get to that amount cos I buy my airtime and data through my banking apps not from the Vodacom apps because I've also been locked out of all Vodacom self help sites, can you also assist me on that. Can you please rectify the error on your system and correct it a.s.a.p. Regards Amos Job ********** 983