What is the best (safe) way to make a payment to Debt Collector (Law Firm) representing a Credit Card Company?

No because they can subpoena the issuing bank and find out if you have a bank account there. Get money orders from the US Post Office. You pay cash, nothing is traceable to your bank account. Also, bank at some some small obscure bank or credit union.

Assuming you do not question the validity or amount of the debt owed to the debt collector, I agree with my colleague and would send a money order.

I agree with the previous two attorneys. Money orders is the way to go.

I agree that a money order is the best way to go, but make sure you keep the receipt if there is a problem with the payment. Also, if you are paying this off, they won't have to wait for the check to clear before the debt is considered satisfied. However, if you are making payments and they haven't agreed to accept those payments, the creditor can still proceed to take legal action against you.