United hijacks father's booking

We booked our flight in Sept of last year with LH on the LH website and are flying the main part of the trip on LH. The dosmestic routs in the US are on United because LH does not service the final destination, We are also members of the M&M.

My dad is however doing a detour on our return trip while mom & I fly home. Somewhere between now and last Sept United changed a flight on dad's itin and ended up cancelling the TA and LH part of the return. United reinstated it at some point but now when I had to change something on his flight and called up LH (remember I booked it with them, paid them and have their booking data) I hear from them that the booking is no longer in their stock and that they can no longer touch the booking and I now have to deal with United.

I wonder will this affect our milage earn too?

Now that I have had to change his final return and I have ahd to deal with United they wouldn't rebook him on a LH flight and would only book him inot the UA flight to Frankfurt and this is the part the chips me off since I expressly booked LH because of the earning capcity. I view this hijacking of the booking without consulting me quite dimly and will make sure I avoid UA expressly in the future.