Tax office computer system problem

Last week I received a letter to my home address saying the ATO couldn't contact me earlier because they did not have my current postal address and asking for money. At first I assumed this was a scam, as the ATO has had the same address on file for me for decades. But I called the Tax Office to check. There was a26 minute phone queue and then further confusion as the reference number on the letter I got was not recognised by the ATO system. However, after that the ATO confirmed they sent the letter, but could not provide a reason why the address had disappeared from their system. I can only assume that this is because the ATO recently changed their computer software and they have not yet got all the glitches out of the system.