Dont know if this exchanger is a trustable one tho, I would suggest for you to just use the known/popular exchanges in the cryptocurrency market, some of them are actually offering or has an service which allows you to buy cryptocurrency with fiat currency or in short, over the counter things and you can use credi cards, debit cards and even paypal.

For example is Kucoin Exchange, its one of the most known cryptocurrency exchange in the market if you haven't heard that one, you can buy Bitcoin, Tether and Ethereum with the fiat currencies like USD and many more. You can read this one  if you want to learn it..

You can then trade your  Bitcoin to USDT trading pair or maybe the other pairs