Vox down grade and syncing problem

I would really like assistance. Vox has given me terrible service way worse then telkom. I have requested a down grade multiple times as my 20 mbps line is to far from the distribution box which cause syncing problems . I filled in a down grade contract and it was excepted by vox with reference number. Two months after signing new contract for a down grade, vox still billed me on my 20 mbps line. Nobody could help me, called in multiple times yet I was told They will call me back which never happens. I only made payment based on the new contract as stated yet vox feel obligated to take out funds out of my account even if new contract was accepted which lead into breach of contract by vox. I am frustrated at this point of time and would like to know how does a person go about this matter?