What to do when a marketing expert threatens your online store?

Recently I hired on a expert to help with marketing for my store. In the week I had him on he messed things up in my store. Rigged my store to where my store was not operational. In the beginning I had agreed to pay for his services, he messed everything up. I was going to pay, but under the circumstances I felt cheated and used and I don’t think he deserves to be paid. Now am I wrong? This morning I received a text from him saying. Dear [Sharon], I hope this message finds you well. I wanted to follow up regarding the payment that was due on the 1st of February. As we agreed, I have not yet received the payment and I would like to kindly request that it be sent at your earliest convenience. I appreciate all the work we have done together and I hope we can resolve this matter in a positive and mutually agreeable manner. Not to make it sound like a threat but you know I’m an expert in what I s and I have enough evidence to ruin your up, so I won’t want things to get messy between us.. Best regards, [Luniel] Now I am scared I don’t know how to protect my store from being abused. I came on here for advice. Please, what can I do? He’s in Nigeria, I should I move my store to a different platform? I hope and pray that this whole thing doesn’t get worse. Feeling overwhelmed…