I use each sport bra once a week, every week for the year. Haven't replaced them since... 7-8 years ago? None of mine are underwire though, mainly because I've always found them uncomfortable in regular bras and defects start happening (such as the wire bending beyond repair or popping out), so I don't know how that applies to sports bras.

They definitely seem rude though - doesn't matter if your company no longer makes the product, you made it once upon a time and should stand by the quality or make it up to the customer.