I ordered a tab on Monday for my son and paid through their payu secure payments app and they told me that I need proof of payment to prove that I paid the money to them

I ordered a tab on Monday for my son and paid through their payu secure payments app and they told me that I need proof of payment to prove that I paid the money to them. I sent them my bank statement showing payment was made to them and the payment allocation from my bank account which shows same and they refuse to accept it.