incorrect account number investigated

ElCabo

First timer so bear with me. 
I've lodged a ppi complaint and the bank has found in my favor under a couple of accounts and sent me the documents to sign for my refund. However the account i was most interested in was a business loan account which over 4 loans amounted to over 500k in borrowings. This came back as no evidence found - however, the account number referenced was a digit out. I have called several times to try and ascertain whether that means they didn't look into the account or whether it was just a typo. But its like pulling teeth, keep getting told that its not their department and they'll log a call back, but that call never comes. Any advice ?

[Deleted User]

Put it in writing

Keep in mind that the PPI scandal was largely related to personal debt, a business debt may well have had commercial requirements where if you didn't have insurance, you didn't get a loan. Also depends when they closed the account, more than 6 years ago and they'd probably have deleted their records, so you'd need to send them copies of your evidence of the loan