Hi All!

This september i flew Frontier from IAD to MCO. DDeparting IAD i saw that a piece of the plane was missing under the wing on the right side of the aircraft
Ground staff were pointing at it as we started the taxi and i was nervous but was of course sure that everyone knew about this.
When we landed in MCO ground staff immidiately started taking pictures of it when we reached our position.
Upon landing in MCO i alerted the staff and captain and showed them the picture of the missing piece. They reacted with surprise, and they didnt know about it at all! The flight attendant even said to me that i should have said something earlier, as if that was my responsibility. I was scared the whole way, but when i found out that the captain DID NOT know about it, I started sweating! I am a nervous flyer and this has just made it much worse.

I got the following lame reply from Frontier:
"Hello Valued Customer,
Thank you for letting me know about your stressful flight on September 23, 2018 when traveling from Washington DC to Orlando. I'm really sorry to hear that you experienced distress due to something that you noticed prior to take off that the flight crew seemed to be unaware of.
Safety Is Our Priority
At Frontier, we are focused on providing a good experience to our customers and ensuring that our aircraft are safe, something that can often cause delays or even cancellations. Please know that our maintenance staff examine our aircraft carefully to ensure that we are ensuring the safety of our passengers. In tracking the aircraft that flew this flight on the date you provided, I have been unable to confirm an issue that matches your description
Customer Care"
Feedback like yours allows us to better identify areas needing improvement and I appreciate the time you have taken to help us out.
We Hear You
Frontier has a hard earned reputation of providing excellent customer service and it’s disappointing when we receive reports of anything less than that. Nevertheless, I am grateful you brought this to our attention, so we can take appropriate measures to ensure your experience is not repeated.
Come Back Soon
We appreciate your feedback as we are always seeking ways to improve as an airline. I'm sorry that you were distressed by what you observed, however we have an excellent safety record and I'm confident your next experience with us will be a good one!
Regards,"

Im really not satisfied with that answer and somehow feel that they should be held responsible. What can i do about it? Was i right that this is a security concern, was I in danger? Why didnt ground staff react before takeoff, even though they clearly saw it? Im not from the US so dont know who to contact.

Hope some experts in here can make me relax a little