Standard Bank double charged me and won't admit it

I had a personal loan with SB. On 17 Feb I paid the outstanding amount on the loan into the account and the account showed R0. I then phoned so-called premier banking and asked what outstanding interest and other fee's were left, so that I could pay that and close the loan account. The lady I spoke to gave me the outstanding interest amount and I asked her to put it on my current account and to close the loan account. She did this and I received sms showing the amount was deducted from my current account. On 3 Mar I see on internet banking that interest, admin,credit protection was charged to the loan account at the end of Feb. Interest was same as I already paid on 17 Feb. I phoned SB and told them about it and they said they will fix it withing 3 work days. 20 Mar I phone them and escalate since I have not heard anything from them. Today I get an email from \Premier banking"saying that I never paid the interest and they will not reverse the charges. Even though the interest that I paid shows on my current account statement. This is how you ***** up a relationship of 23 years! I am tired of having to phone them almost on a weekly basis to sort out their mess. """