Unauthrized charge

My may 2016 bank statement includes a supposed service or good charged to my Visa for $29.99. The charge was made on 04/18, de reference number is 19134752448, the item allegedly bought was “Dri*Avast Softw” by “Shannon, Co.”, to whom I don’t know. I hadn’t buy any service or good from Avast in May 2016 nor in any other time. I request a refund for $29.99 to my Visa and stop charging any future item to my Visa Card not authorized by me. Please, keep me informed.