Rising damp discovered on day of completion!

Hi,

I need some advice, please can anyone help?

I very recently purchased the freehold of a pair of flats and the leasehold of the upstairs flat to rent out. On the day of completion the leaseholder of the downstairs flat told me that she has rising damp and that she had repeatedly told the previous freeholder.

So,
1.) should the freeholder have told me prior to the sale?
2.) is it my tough for not getting the downstairs flat surveyed?
3.) who's responsibility is it to get any work done?

Can anyone advise on what to do next?

Thanks