Accused of bumping car two days after I returned it

Two days after I gave the vehicle back (and the vehicle was inspected when I returned it), I got an SMS from Europcar with pictures of scratches on the left rear bumper. I have tried to dispute this, but Europcar has not been supportive or helpful. Anything could have happened during that time. Today, I got an SMS saying I owe them R4098.25 (reference ***4). Please assist as I feel like Europcar is taking advantage here. I don't know what the extra R98.25 is for as I returned the car with a full tank.

I would like to have my deposit of R1750 returned as I have done everything as per the rental agreement.