Power of Attorney fees

Pibs

 I sent forms off for a Power of Attorney earlier in the year. Due to my income of £7000 I was able to apply for a reduced payment saving £82. The POA was returned to me in February even though it didn’t require any alterations to it. The letter stated that I had not provided sufficient evidence to support the low income refund as I had sent tax forms etc showing my yearly income which I thought would suffice. I duly obtained the evidence and returned the information in March. I have now been asked to pay the full amount as I am now in receipt of the State Pension which puts me over their £12,000 threshold for a reduced payment.  There were no alterations required to the POA so that was fine when originally posted and the forms plus evidence were returned to the Office of the Public Guardian again, well before the end of the 20/21 financial year. I was just wondering if the cost should be based on my income when I first submitted the POA, i.e the 20/21 financial year and my income then? There were long delays in correspondence from the Office of Public Guardian, probably the result of Covid working practices etc.
Any advice concerning this would be appreciated thanks. Kind regards.