When you place an order, it'll show you the USD equivalent of BTC. Did you check that at the time of placing your order? BTC pricing is inconsistent, so if you haven't checked pricing at the time of placing your order and maybe checked it before or after that, it's possible that it was 917 and not 981
What I meant is, the BTC price at the time of placing my third order was about 981 USD, but it was not updated on the Bitmain website and I thought it was a technical error. When I spoke to the Bitmain customer team about this, they said the price gets updated every 10 mins on their website and many other orders were taken for 917 USD during that period. Although I wasn't convinced with their reply, I didn't want to argue further.