charges made to my mastercard

I have been charged three times in January $59.99,$34.98 &$23.99 which i assume were supposedly charges by Avast for computer security.Ihad only ever approved the $34.98 to be made against my account.Also they have asked for more money this month to cover security.I require a full explenation of all the charges before I will allowany monies to be taken from my account