Unauthorised purchases bank charges

It's been more than two to three 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 "#Uber Sa Help.uber.c " and this issue has happened in july and they told me to change a card i did all of a sudden its happening again and this time around its happening even on my easy zero

i would like to know how can i make a purchase from this sites or apps if i know i dont have funds this is getting on my last nerve now my bank charges has increased to R117. the only delcine that i have is for your funeral policy and after that i dont know whats is happening.

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 because i will be having issues with my meal allowance from school.

Help ASAP