What to do?Have i been scammed by NTS global services?

Here's my story.About a year ago my computer became infected with a virus or so it seemed.I called the number that was given in the pop up.I paid them 400 plus dollars by prepaid visa and let them take control of my computer.Global services called me up today saying there going to give me a refund because they are having problems with software.So i allowed them access to my computer.The tech guy said he will transfer the money into my account and asked me for the last four digits of my debit card which i gave to him.However the transfer could not be made because my checkings account is in the negative.Tonight i was thinking about this and out of curiosity i typed in the company name and found they have been associated with scaming people.The questions that come to mind should i get a new debit card number and password for online banking?I would like some advice and i look forward to hearing your feedback.Thanks