Thanks for the suggestion, I will contact my credit card provider as you say.
The response from LH has usually been "we're dealing with it", but nothing ever comes of it. Sometimes they tell me to contact LX, which makes no sense as it is ticketed and purchased from LH. They sometimes respond as if it is a EU261 compensation claim, which isn't related to getting the ticket refunded.
I had many flight issues over the years but never had such a problem to get a simple refund!