What to do when university has not yet reimbursed travel costs for a job interview?
In general, don't attribute inaction to malice or fraud when it almost certainly is just due to laziness, disorganization, or incompetence. University bureaucracies, especially in some countries, can be unbelievably slow. Sadly, three weeks is often not a particularly long period to go unreimbursed. Be patient and persistent and this will almost certainly work out eventually.