A website that does both or would different websites work? BTC to Monero works really well on
ChangeNow or
SimpleSwap, just don't do anything stupid to trigger the system like visiting it with TOR or sending tainted coins. You can use a residential proxy for something like this.
It's best to stay away from anything associated with ChangeNow. They have a long history of unresolved scam cases, and your transactions may be frozen or your KYC request may be required for no reason. You can find a better list here --->
https://kycnot.me/ or post in this board:
https://bitcointalk.org/index.php?board=53.0 (you need to go first because of your trust).
If you have a millions of transactions, some are bound to be problematic such is the nature of numbers. As of date I know not of a single credible scam accusation against ChangeNow, and I have never heard anyone get scammed from my contacts who have volumes in the millions. These days everyone I know uses ChangeNow. A lot of those "credible" scam accusations are people who sent stolen or hacked coins to get exchanged thinking that they will get a quick swap. Next time the user should read the terms of service before blaming the platform for expected behavior.