What can I do?
In addition to the answer by @luchador, keep contacting the airline, asking about the status of your complaint. In some countries you just send a complaint/request one time and then wait to be contacted again. That is not how it works in all countries. In many countries (including the one I live in) you often have to fight to get a proper response.
Contact them many times. Always ask for the name of the person you're talking to (and write it down). If you get rejected or stonewalled multiple times, ask to speak to their supervisor. (Also, if you get this far without being reimbursed: To answer your question: Yes, by that point this would per definition be a scam by BoraJet.)
Email a link to this question to BoraJet
If such repeated contacting and complaining doesn't work, email a link to this question directly to BoraJet and explain that it's written by you due to said case and the fact that previous efforts have failed. (You can also leave other negative reviews online and include them too.) Show them that their policy/cheating is having a negative effect, however slight, on their reputation. It's actually not as innocuous as it may sound. Imagine if this question hit the Hot Network Questions here and got 10.000 views. This question has now hit the Hot Network Questions here and has a lot of views and upvotes.
Also:
If [SE says] a question has 1,000 views it probably has at least 2x real
world views, and potentially as many as 5x real world views.
It could end up showing up does now show up in Google when people search for BoraJet (and could even end up being is now the second hit for "is BoraJet reliable." (I tested this in incognito mode.) This is not something BoraJet wants. It's very bad publicity. BoraJet may actually take notice and choose to reimburse you, asking you to update the question.
You could even find what common searches bring this result up and include those links in the email.
As @Willeke suggests in a comment, you could also post a link to this question elsewhere online, like social media, travel related sites, etc. Anything to get attention to the case helps you when you've already tried and failed while contacting BoraJet directly.
It is, however, difficult. I'm assuming you don't have the name of the manager who promised you to pay for the ticket. (If you do, you can call customer care and refer to him directly.)
As @JonathanReez says, if all of this fails your last resort is indeed to complain to your credit card company and accept the 85% loss.
In the future, when someone makes a promise like this, ask to get it in writing.