Tommaso Madonia

Hello, I'm a freelancer/sole trader currently working for a EU based company and I get paid weekly in pounds. Every week I receive £12 less than I invoiced and my client claims this is due to some bank transfer fees. They are now asking me to invoice for £12 more to account for the difference. In my books, should I consider these bank fees as expenses even if it's not my bank charging these fees? I have no proof that the a bank is charging these fees and the client is not just sending less than it's due. Thank you!