Is my high school diploma fake?

I am from a Nordic country, I took an online high school course in 2021, which is called AIU high school Florida, and in 6 months I was done with it.

The reason why I’m thinking that it might be fake because, when I applied for the school the teachers were so kind and gorgeous, answering all calls and emails, but since I paid the $2500 for the course, nobody did answer my emails, I did contact another students and they have the same problem. Also if I did study in my home country, it would probably take me 3-4 years to complete my high school program, but I think 6 months is too short.

The only time they answered me when they had to send my diploma, and I asked them for an online copy as well, but they told me that I need to pay extra for that.

I wanted to put an attachment but this community doesn’t allow it.

Could you please help me figure it out?