It sounds like you are eligible for 400 Euro compensation.(EU flights >1500 km) for delay (delayed more than 3 hours) under EU Reg. 261/04. IT issues should not be considered an extraordinary circumstances exempting LH from paying comp. Try Google EU reg. 261/04 to find the regulation (but it does not state anything about delay!)
Fill out out the form on the LH. webpage explaining in short that on 16 MAY you were delayed on LHXXX and had to be rebooked to later LHXXX flight to BLQ and thus delayed for more than 3 hours. Most likely LH will reject the claim (LH does that to all claimants regardless of the nature of the claim) so some persistance is needed. Reply back, argue why LH is wrong and ask for the comp. again; in most cases you will get it the second or third time unless LH really is of the opinion that there is no obligation to pay as the delay was caused by extraordinary circumstances outside the control of the carrier. Good luck!
As already pointed out airhelp or other claims agencies could also be a solution if you dont want to deal with it yourself. Their services are on "no cure no pay" basis and they keep 25-40% of the compensation for their services.
Last edited by SK AAR; May 17, 2018 at 2:43 am