I have done it as well - took 2 months and a few phone calls, letters and emails.

My miles posted to AC. Several letters to AC finally got them to remove the mileage from my account. Then I took my statement showing the mileage reversal and sent that with my BP to LH and the miles were credited.

It was the angels at LH that told me how to go about it.

Be persistent.

Same thing happened this year, but as it was only for about 6K, didn't worry about it. The above AC example was for a C flight that with bonuses would be 48K on LH, not a small sum at all.