Disgruntled Client

I had just received an sms from credit intel saying I owe R273.63 as per attached statement on the 11th I spoke to Selina and said the account will be paid on the 23rd of December R218.01.How can I be charged R55.62 additional interest for a period of 6 days.I tried speaking to Patience instead I got to speak to Thembi who is very rude and I don’t appreciate the way she spoke to me.I promised to make apayment and yet they load more interest on account wher they emailed me a statement saying how much payment will be.