I have read the FDCPA thoroughly and do not see where the creditor or collector has 30 days to validate a debt. I see that you, the consumer, have 30 days to demand validation. Where is the interpretation that the creditor/collector has only 30 days or the debt is invalid?
The debt collector (to which FDCPA applies) does not generally have to reply at all, if they stop collection activity. If you dispute, they do have to indicate the account is in dispute, if they report it to CRAs, or anyone else. See Sec. 807(8): http://www.ftc.gov/os/statutes/fdcpa/fdcpact.htm#807 If you request validation within 30 days, they cannot assume the debt is valid until they obtain and send validation from the OC, so they cannot "continue to collect" until they validate. Collection activity may include reporting to CRAs, or verifying disputed debts to CRAs. Some state laws impose stronger requirements. For example, Texas specifically requires validation within 30 days. Some courts have interpreted the FDCPA language as specifically requiring validation within a reasonable period, perhaps 90 days.