Do I have to pay gas fees when buying ETH or another ERC-20 Token on my Trust Wallet via Simplex?

Hey,

I just bought 50$ worth of USDT ERC-20, which was a mistake ( I wanted BEP-20 )

I paid Simplex 55$ and got 48$ (I think I paid fees here) – but my wallet says transaction fees of 100$ (wt???)??? But I haven't paid 100$ in gas fees, I dont even have ETH in my wallet.

So when buying via Trust Wallet they say that they are partnered, so they have some kind of system that they wont charge any transaction fees? I mean this would be stupid lol. Its not going to another exchange right?

To be direct:

I dont have to pay 100$ now for my mistaken bought 50$ ERC-20 USDT right?

Simplex haven't mentioned that.