Voice mail

Have a customer who used Ring Central - we are an after hours answering service. Their call log shows call coming to us and then it says voice mail but we do not offer voice mail. Assuming the voice mail is coming from Ring Central but the customer says they don't have voice mail. We have records of calls coming to us but their patients say they left a detailed voice mail. Cannot convince our customer that the voice mail is on their end. Need help understanding the call logs they have sent us.