Telkom Mobile charging axtra money

Good day

I have done a cell phone contract with Telkom mobile in November 2016 for 24 months contract ended November 2018. I have paid R803 on my last payment an it was extra amount of R303 wich they have sending me sms that thy will give me refund of R303 .

But Telkom mobile is currently sending me statement that I am outstanding amount of R368 . I have a prove of payment and bank statement that clearly shows that I have made payment. Can you please help, my cellphone number is ********** 554, ID no ********** 798089.