There are a number of formulas used when complaining in English. It's important to remember that a direct complaint or criticism in English can sound rude or aggressive. It's best to mention a problem in an indirect manner
:Here are some of the most common
...I'm sorry to have to say this but
...I'm sorry to bother you, but
...Maybe you forgot to
...I think you might have forgotten to
...Excuse me if I'm out of line, but
...There may have been a misunderstanding about
...Don't get me wrong, but I think we should