Make sure your certificate file is listed under the relying party’s encryption tab.
For example, if the certificate configured in your service provider’s SAML configuration were sp.pfx, the corresponding sp.cer would be configured under the encryption tab.
If there’s still an issue, please email us a screenshot of the ADFS relying party’s encryption tab showing the certificate’s details. Also, enable the SAML trace in your service provider and include this in the email.