Haven't had that happen to me, but I did get asked by a clueless support rep from $VERY_BIG_MULTINATIONAL_CORPORATION whether I was also an employee due to their company name appearing in my email address. (Coincidentally I used to consult for that company.) Long story short I set them straight rather than trying to parlay their ignorance to my advantage.

The most shocking thing was that I was calling them regarding an issue in which they required me to prove my identity, and yet the person I spoke with didn't seem to be well versed in security measures.

Also: I use a separate alias for every company (and sometimes individual) I deal with. In the 25 or so years I've been doing this, so far I'm up to over 1,000 aliases.

I've always knew at least some companies would do that so I just use slight variations on their names. Never had an issue.

I had this happen as well. I responded with a long rant, which apparently proved my humanity.

Linode did this to me.

Just another data point, I've had the same issue with some vendors.