I have a complaint about my order.
Is this sentence used in any situation when you have some trouble with the product you bought? To me, it sounds very straight, but I'd like to know if it is OK to use it or not. Thank you in advance.
This is usually used in a restaraunt, after a mail order purchase or such, where you actually place an order for something and then have a problem within that activity. If you bought something at a store and took it home, and then found some problem, you would say
I have a complaint about my purchase.
If you think complaint is a bit harsh, you could say
I have a problem with my order/purchase.
or you can soften the assumed responsibility...
I think I have a problem with my order/purchase.
If you want to complain in English it is best not to come out with it straight away, so use a longer sentence that introduces the problem slowly. Short and aggressive:
I'm complaining about my purchase.
The verb should not be aggressive, but softer and indirect:
I have a complaint with my purchase.
It is also a good idea to make it impersonal:
There is a problem with my order.
Or even doubtful:
I think there is a problem with the order.