The right action to get labour rights and visa cancellation after resignation

Hi,

I am working in the UAE for the last 1 and a half years, I resigned from my company but they are not giving me my passport back.

I have already completed my notice period but now the old company is asking me about the new company offer letter, visit visa or employment visa.

But the question is how can I get a new visa if they don't cancel my visa?

One more issue is that when I submitted my resignation letter to HR, he asked me to send it to the CEO using Whatsapp.

I sent it on WhatsApp to the CEO and then HR told me it's accepted, so I don't have any proof also if it's accepted or not.

What if I show the new company offer letter can it create a problem for me?

I am stuck now. My passport is with them, final settlement and everything. I need advice on how to solve this issue.

Thanks in advance