If your current employer has repeatedly acted in bad faith, I wouldn't worry too much about burning bridges. Your answer is fine but probably invites challenge. Saying "Thank you but I have made my mind up" is still polite but leave less room for debate.

Someone wiser than me said: "You never burn bridges. You either leave them standing, or you blow them up with not a bit left".

No need to bring up "good faith". It's not "good faith". You've already accepted another offer. That's the end of the story. "Unfortunately I've already accepted the offer from the other firm."

Have you actually accepted a new job offer? Because lying to your employer is certainly not "good faith".

@Gh0stFish It's neither good faith, nor bad faith. The OP's life after they leave is NONE of the current employers concern.

@Gh0stFish Of course.

@GregoryCurrie absolutely - which is why it's fine to not answer that question, or to say "that's none of your business". But that's completely different from lying to them about it.

But what would make you stay? Just because you have already signed somewhere else does not mean it's impossible to reverse that decision.

@Philipp nothing. There is no trust anymore.

Then why are you afraid of "burning bridges" you wouldn't want to ever cross again for anything?

@Philipp I can cross with the same people at other firms. The problem comes from senior management, not immediate managers.

Per update: yes it’s a tactic. Repeat “my last day is x.” Then leave on X.

@user121416 100% reiterate your last day. Don't have your notice phrased in terms of X weeks, have it phrased in terms of a specific date. Don't let them create a situation where they can paint you badly to former co-workers/references over inadequate notice.

@Gh0stFish You can say lying is bad. And maybe you have a point. But that's not what "good faith" means.

@Gh0stFish Good faith: "honesty or sincerity of intention". Saying you have another job lined up does not give a false sense of intention. It's just a lie. If you have no intention of negotiating, then lying to prevent them from even trying to negotiate may even be a sign of acting in good faith. In other words, it is possible to lie in good faith.

In case you are in any doubt, an employer does not have to accept your resignation. You have resigned. Unless you change your mind there is nothing they can do about that, and your resignation takes effect on the day you said it would.

What country are you in? Does it matter, whether the company accepts your resignation,, assuming you have terminated the working relationship as written in your contract?

Related: Can an employer refuse my resignation?

Regarding your update: you’ve given notice. Your last day will be the day you’ve put in your letter of resignation. The company have that time to replace you, if they don’t that is their failing and not your concern.

What is "w.r.t" ?

@Itération122442 With Regards To

@GregoryCurrie Thanks. Well. It's not that long to write. Why using this ? Not everyone is native english speaker, let alone acronym...

@Itération122442 It's takes 10 seconds to google. WRT is reasonably well-understood.