My question involves criminal law for the state of: Idaho

I was caught shoplifting ~$13 worth of merchandise at Walmart about a month and a half ago. The police were not called. I was told I would have to pay a fine and they gave me the number to call. I paid the fine in full right over the phone and a confirmation receipt was sent to my email. However, I have been receiving calls from Walmart's collection agency, Bennett Law. I have not talked to them, they never leave any messages identifying themselves and the only reason I know it's their number is because I searched it on the internet. They are starting to call more frequently. I have never received anything in the mail from them or Walmart. I am tempted to block their number but I don't want to piss them off so that they start finding more ways to contact me. I've read many things saying that they try to scare you into paying more and more money. Is there any advice on how to get them to leave me alone since my fine has been paid?