Ironic

i·ron·ic/??ränik/

Adjective:

Using or characterized by irony.
Happening in the opposite way to what is expected, thus typically causing wry amusement.

Today I received a helpful letter from the Taxman reminding me that I need to make sure that I supply them with all my correct details to make sure I pay the correct amount of Tax. Ironic really as I just received a cheque from them due to the fact they got their calculations wrong five years ago!