Who do I complain to at Barclays

Son was promissed an extention to his loan to cover a Barclay card and loans, bank gave him false hope the consolidation of the loans would have freed up £126 which would have helped him

Instead the person making the comment passed it to another branch, who declined the loan extension...even though he has a lot of money each month surplus in his account according to the bank this made him a good risk because he can easily pay for the loan extension

Thanks to all for reading