Maybe they're busy and honestly $5500 is a large amount of money.
Well bitmain is not scam maybe they are busy to assist all their customers and all their hardware is in demand this year.
Just keep contacting them and send a ticket about your issue so that they are aware about you.
Honestly, bitmain these days were getting worse because the quality of their miners compared before is different.
Their customer service response is too slow.
I think their customer service is fine but because of many newcomers that investing in mining, this might be the reason for their slow response.
But they are still legit and selling a new product that can mine with both altcoin and bitcoin.
Just keep contacting them they will response sometimes in instant sometimes 3 days.