It's a big Scam. Telephoning the number will give you a free scan of your Computer and there will be dozens or even a hundred or more infections in your Computer, which perhaps, in reality, only has the Malware which has been introduced by the Scammers. You will then be offered the opportunity to have your Computer 'Cleaned-up' for a fee and your Bank account might then be cleaned-out; after you make 'on-line' payment.
If you haven't already got Malwarebytes then download the free edition and save the file to your downloads folder. Install from there and run a Scan; which might take as long as an half hour or more. Refuse all offers for the Premium edition and anything else on offer.
https://www.malwarebytes.org/
Please report back.
Hans.