UKVI Student Visa Bank Letter

I urgently want to apply for a UK Student visa for a dependant (self sponsored student). UKVI require a bank statement and a letter that states a certain amount has been in the bank account for a consecutive 28 days and the cash is available for withdrawal. I went to Capitec Clearwater in Johannesburg on the 2nd of July, 2021. Went home with only the bank statement. But letter is required too. How have other parents, banks dealt with this requirement. Hasn't there been a self sponsored student from South Africa? I'm pleading with other students, parents or Ombudsman to give me advice!!!