HR team claiming that I have misbehaved with HR over a call by abusing and they want an apology email

My last day at my current organization has been completed and I got a call from the separation HR team claiming that I have misbehaved with HR over a call by abusing and they want an apology email else they will not give me the relieving letter, Is this possible? HR was rude too.
Pls suggest

One question is, did you misbehave or shout at / abuse them?
If not, why will someone make such a claim? You need to give us the proper background.
Secondly, do you really have much of a choice?
Third question, even if you were to give an appology, what is the problem with that? What are you afraid of?

What if gr can use it as written evidence for some more ego revenge, ?

Only thing I did was to shout as shut up then nothing more

You have not given the details of what happened.
In that case how do you expect someone to advice you?
If you want proper suggestions, you better put the relevant details

You require the relieving letter more than the HR needs the apology letter. You also admit you raised your voice when dealing with HR ( perhaps in a fit of anger/ annoyance)
I suggest you give an apology letter for raising your voice with HR and complete the formalities and move on with your life.
Don't make the apology letter an ego issue because from the limited facts you shared, you were not completely blameless even if you were provoked by HR.
Best Wishes

Thank you for your suggestions, i have made a call to the HR and explained the situation and apologized for raise of voice, she was proactivily understood and accepted it ... problem solved