I have tried depositing USD from my revolut account to my USD denominated Saxo account. But my funds seems to have been refunded back to me. Have anyone encountered such issues before?

Saxo no longer allows 3rd party fund transfers, you need to transfer the money from an account in your name. You will have to either deposit in SGD and pay the 0.75% currency conversion fee, or use a multi-currency account in your name to transfer USD to Saxo directly (which will incur fees depending on your bank).

I suggest switching to another broker - SCB, IBKR and Tiger Brokers are what I normally suggest.

From their website:

Saxo Markets does not accept incoming funds from any third party. Saxo Markets will only accept funds originating from a bank account held in the same name registered with Saxo Markets. This rule applies to both individual accounts as well as corporate accounts.

Funds received from any third party accounts will be returned (less bank charges) to the sender. The funds should typically reach the sender’s account within 5 to 10 working days, however, there may sometimes be a delay depending on the banks involved.