I say keep quiet for a little longer. Did they tell you specifically what they were sending or was it just a vague ‘oh yeah, we sent you something’? Any chance they just said it and didn’t really mean it?
I'd keep quiet a bit longer. Who knows, money could have been tight and it might come later. Or it could have been said with little intention to follow through on delivery. Regardless I'd stay quiet until they bring it up. At that time you can acknowledge never receiving it, or claiming to have completely forgotten to expect it hence not bringing it up.
Was it an "oh yeah, we should do this again" or was it a "can I take you out tomorrow night" kinda deal? If they said they mailed something and it's been a couple of weeks then yes, ask. If it was vague, no.
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