How can I win chargeback disputes over undelivered items?

Hello,

We’ve recieved quite a few chargebacks over the past few months for item not received.

We send all items via Royal Mail Tracked with proof of delivery and GPS tracking, even with a photo of the customer’s front door we are still losing the appeal.

What do we need to do to protect our funds, as this seems to be a loop hole for scammers?

Thank you in advance.

Pete