iFastNet sells their services in USD, which is clearly shown everywhere on the product information and during the order process.
If your payment method is in a different currency, then your payment provider will handle the currency conversion. Which exchange rate they use, or which markups or additional fees they charge, is up to them.
All of these conversions and fees are entirely hidden from the merchant: they just charge USD and get the USD amount charged. So no, it’s probably not possible for iFastNet to say exactly how much you will be charged by your bank ahead of time.
Did you get the order confirmation through email? If not, then you may have entered an incorrect email address during the order process. I’m not sure exactly what iFastNet’s process is for this, but I suggest contacting them through their support portal at https://support.ifastnet.com. Note that you will probably need to sign up for a separate account there.
Did you literally choose “a.xyz” as your domain? That’s not a placeholder?
Then it sounds to me like you only bought a hosting account, not a domain name, because it seems unlikely that this domain was available for registration.
Through the iFastNet portal, you’ll have access to cPanel where you can create the email accounts.
No, iFastNet has their own pool of subdomains for premium hosting. A check on their website tells me the following extensions are available:
OO.GD, ES.HT, AR.NF, CC.NF, IN.NF, IT.NF, MX.NF, RO.NF, RU.NF, UK.NF, WEBS.NF
What @KangJL said.
However, it sounds like you purchased a premium hosting account already. If so, I would just host my website on that premium hosting account instead.