If the debt collector has been assigned (in the contract sense of that work) the debt, NOTHING in the FDCPA applies to them. The FDCPA only applies to third part debt collectors.
If the FDCPA does apply (the debt collector is collecting for a third party), they're not obligated to show you anything either. The debt validation rule in FDCPA just says they have to double check to see if the debt they are trying to collect and the amount is correct. It doesn't mean they have to show you anything,