In recommending the purchase or replacement of any Medicare supplement policy or certificate an agent shall make reasonable efforts to determine the appropriateness of a recommended purchase or replacement. Any sale of a Medicare supplement policy or certificate that will provide an individual more than one Medicare supplement policy or certificate is prohibited. An issuer may not issue a Medicare supplement policy or certificate to an individual enrolled in Medicare Part C unless the effective date of the coverage is after the termination date of the individual's Part C coverage.