Foschini Threatening texts but account was never in arrears & payment made as per statement

I received an sms from Foschini thanking me that i have paid my account in advance on the 29 November,they said i must pay R363 and i went to the store same day i paid R500 but now since Monday they have been sending me threatening smses that they will take legal action against me for R363. I have sent proof of payment of R500 but i still receive threatening smses and they are not replying to emails.

What legal action are they going to take because my account was never in arrears from the start. Im soo disappointed & i feel like paying the balance and close that account.