Declined Purch Tra

It's been more than two day now that I am getting FNB InContact Messages stating that. FNB Transaction on account ..478298 declined due to insufficient funds. Follow the link below to view offers available. FNB a Div of FRB Ltd FSP3071. Then all of a sudden after two day I see in my transactions statement stating that "Declined purch tra" which I believe purch stands for purchase. yet i didn't make any transaction nor have debit orders on my account for the dates these "declined purchase"are made. Now this increases my bank charges as im being charged R8.50 per purchase for every decline that takes place which I can say that isn't even my fault unless proven otherwise, im very upset by this! Because its putting my account on minus -

I would like you to assist me with this I have even blocked my card been afraid that when my school allowance comes through whatever that is declining will take my study allowance.

Help ASAP