Telkom debited more than the contract amount!

Can Telkom explain to me why on earth would you debit me R200 all of a sudden on a R99 data contract i have with you, and then when i reverse this amount as an amount i did not agree on you then tell me i need to pay R500 plus to avoid suspension ? From R99 to R200 to R500??? How did we get here? I have been a loyal customer to you for years and now this??? I am so upset!!!