Tenant complaining of pet urine smell after carpet steam clean

[Steve S.]

tenant called and asked if they could steam clean the carpets. I told them I had them cleaned before they moved in and asked why they wanted to?  

They went ahead and had them cleaned. Now they say because they were steam cleaned it's revealed a stench the steam cleaners say is in the pad under the carpet allegedly from a pet from the prior tenant.  

What do you recommend I do?