Truwotrhs is messing up my credit score

Truworths is messing up my credit score.I have made my monthly installment on the 30th of April via EFT.I only found out on the 12th of May that the reference number I used was incorrect and I called more than 10 times at Truworths and sent e-mails more than 5 times with the proof of payment attached.I even spoke to the the Truworths supervisor at the call centre on the 16th of May.They have not allocated the payment on my account and my account is still on arrears and messing up my credit score.Truworths needs to sort this out it's almost 5 weeks now.