The call is a tactic. Your rights are a constraint the caller prefers you do not exercise.
When the MCA funder transfers your account to a collection agency (or assigns collection duties to a third-party firm), the nature of the contact changes. The agency operates on commission or on a purchased debt model. Its incentive is to collect the maximum amount in the minimum time. The methods it employs are calibrated for speed, not accuracy, and the legal boundaries it observes depend, in uncomfortable measure, on whether the debtor is aware of those boundaries.
You have rights. The caller does not intend to recite them.
The Right to Demand Written Verification of the Debt
Under applicable debt collection statutes, you have the right to demand written verification of the amount claimed, the identity of the original creditor, and the contractual basis for the obligation. The demand must be made in writing, and the collector must cease collection activity until verification is provided.
If the amount the collector claims exceeds the amount your agreement supports (after accounting for payments made, the correct factor rate, and any reconciliation adjustments), the discrepancy is a defense.
The Right to Communicate Only Through Counsel
Once you inform the collector that you are represented by an attorney and provide the attorney's contact information, the collector must direct all further communications to your attorney. This is not a request. It is a legal requirement. Calls to your business after this notification may constitute a violation of applicable collection statutes.