Still not sure
1a - The operating carrier of the LHR/MUC sector is LH. LH advised BD of the new flight and as BD were first carrier they were obliged to advise you the re-booking as offered by LH
1b - new flight was on same day
1c - operating carrier LH
2 - Was an explanation given?
3 - Strike by another carrier pretty exceptional circumstances
4 - It is all taped therefore proof is on file
The RUH/LHR was cancelled because you stated you wanted a refund as the alternative was unacceptable.