Refusal entry Singapore

I want to know more about my friend refusal entry into Singapore because I was terrible at calling the ICA number.

My friend case is before the MCO was opened last year, because his company has been delaying his permit, and he has also done a body check up, and he is also renewal passport in Singapore. It wasn't until Singapore opened when he back to hometown and found out that he had broken the law.... He immediately searched the Internet and told the company, and the company helped him appeal and write the reason is they think IPA can make in become special pass to work. In the end, the appeal was unsuccessful, and then he was directly terminated and no salary was paid.

1. I want to know if it is difficult to make a second appeal after being refused entry by Singapore?

2. Even if the personal did not change the white card, the problem occurred due to the arrangement of the company's HR department. ICA won't accept this reason?

3. If the appeal is unsuccessful, how long is the real criminal law, and when can my friend come back?

Can help me and told me want can i do?

Thanks.