I tried to phone a provider with about 15 good reviews on TER who refreshed her contact info and web ad a week ago. I get a message that "the call cannot be completed". I sent email with personal info to her asking to call me back. Now I wonder, is this safe? Is it ok to respond if she calls me or should I assume that there is a problem and stay away?

It should be OK to take the call. Just don't say anything that might get you in trouble if recordered.