National Do Not Call Registry Customer Service Issues

Today, I received numerous calls, some leaving voicemails, from 1-[redacted]. The voicemail instructed me to call back a number that was unclear to request to stop these calls. Despite calling back and requesting removal from their call list multiple times, I continue to be contacted by this number. I have previously been scammed by this same entity but was able to recover the funds on my credit card. Now, they are threatening to withdraw money from my account again. I have alerted my credit card company to prevent any future charges. However, they mentioned they can only block the merchant if another charge occurs. I am unsure how to cease these unwanted calls and avoid the risk of unauthorized charges to my account.