incorrect billing

hi . I took out contract just over 2 months ago and signed for a specific monthly premium, however today I queried my bill is incorrect. I was advised by consultant Londiwe Sokhela that spend limit of R500 was added. I then advised that I did not request this. she advised this was done automatically.this is so frustrating, I never requested for this and why would Telkom automatically add this and not advise client. I then requested for a refund for extra amount and I was told that it could not be done. I would like refund as this was not requested by me and how dare Telkom add this and not advise and then say I cant be refunded. I signed a contract with a certain amount nothing else..