Company A extended me a job offer verbally two days ago (Monday). They promised to provide me a written job offer letter to review and consult with my parents, but they failed to do so because they're waiting for a start date from their client. What I received from Company A is only a list of pre-employment requirements and it doesn't state anything about job offers.
I have also a job interview the next day (Tuesday) with Company B and passed the exam. On that same day, Company B also extended a job offer and I much preferred to work with Company B, so I accepted it. The time was end-of-business of Company B when I accepted the job offer.
The next day (Wednesday), Company A called me to come over to their office and sign the contract on that same day. I then informed Company A that I have already accepted a job offer, since I was already waiting for Company A's job letter for me to respond within one day, and he also said that they called me yesterday (Tuesday) where in fact they haven't.
Now, Company A told me that they will add me to the blacklisted applicants since I did not inform them immediately if I did not sign the contract on that day. I do admit my mistake of not informing them ASAP. In the end, I didn't proceed to the contract signing and turned down the job offer.
My concern is, will it affect my next employer's application status? Do I really need to worry about its damaging costs in my career?