I'm not sure that we support TLS 1.1 in Pega 7.1.3. Starting in 7.1.6, there is a dropdown on the Connect-SOAP rule that allows you to specify the SSL protocol version to be used. This does not appear to exist out of the box for prior versions.
We are using 7.1.7 version and set TLS 1.2 protocol version in SSL configuration but still it says the same error "TLS 1.0 has been disabled in this organization. Please use TLS 1.1 or higher when connecting to Salesforce using https"