Hi Meg
I don’t think there is any requirement in NSW for the strata manager or EC to even respond to your letters, let alone send you a copy of letters they send to other residents (it’s different in Victoria).
If I were in your shoes, I would send a letter to the strata manager asking them to issue a Notice To Comply, citing the by-law that has been breached and to send a copy to you at the same time.
If they failed to do that, I would tell them I was taking the Owners Corporation to the CTTT to get an order against them, forcing them to take action. That might get things moving.
Chance are, however, they could have sent a letter and just not bothered to tell you. So maybe the best initial approach is to ask them if you can get a copy of the letter that they sent.