closing the one account

lotterywish

hi all

have closed our one account mortgage very recently, however when I spoke to them to authorise redemption figure to new lender, they told me I would have to pay a £75 admin fee + a months interest as I paid in arrears. The admin fee I was fine with, but is it normal to pay this interest payment too? Don't understand why I was paying in arrears anyway?

Should point out this is our first mortgage and first time i've swapped it, so complete novice - apologies if just being naive

thanks for any advice given