Truworths unacceptable customer service

I'm a Truworths account holder for about 25years. Never have I missed a monthly payment. There were months that I pay a few days later, due to unforseen circumstances. Today(15/01/21) I was phoned and told "Your account is in arrears" I politely told the lady, that I already eft the instalment of 2 months(must be only one month) on Tuesday 12/01/21. The reply I received is exactly why I'm complaining here. "Well, it's not on our system and if you don't pay it by this weekend...." I lost it as I have all the proof that this "double" payment was done. After 25years of being a customer, I'm threatened by such a rude person. With a credit of thousands of rands and continously notifying me to spend my money in your store, you ruined this relationship for a mere R350. If your system is not updated with a payment 3days after an eft was done, then the onus rests on you to proof me wrong. You slap me with an interest, way too high, for paying 5days later. You did not even bother to handle me politely or to ask me if there's a problem. Shame on you Truworths.