Vodacom Increases fees without notice and cannot give reasons

I took out a contract with Vodacom in 2017. The contract fees have increased from R398.50 to R458.99 in a space of 18 months. The first increase took place with the VAT increased (which is understandable) to R401.58. However, the fees increased to R448.58 without any notification or reason for the increase. It then increased again to R458.99, again with no notification and no reason given. When i phone Vodacom, they are unable to explain to me why the fees have increased and I have also driven from Alberton to Vodaworld in Midrand and still no one could give me an answer. Now I can't even upgrade because I am told that I owe money on the account. I need someone to urgently contact me regarding this problem and give me answers.