False representation

I am appalled by the service of Telkom Mobile, when I took my contract with them for starters I told them that I wanted to be able to load air time when the free minutes are over which they did not do, and they sent me an sms wanting to increase my limit from R139.00 to R389.00 which on the sms it said reply with a yes or no which I rep**** with a no but according to them they did not receive my response even though on my phone it shows as delivered, my question is this if they knew that with my contract I cannot reply to an sms which they sent me which according to me I did, then why did they not say at the bottom of the sms that I should call the call center to accept or decline the offer.