Avis Car rental damage dispute

I'm being charged R2600 for damage on the front bumper under the vehicle I rented from Avis South Africa. I pointed out damage on the bonnet which the branch missed when I collected the vehicle. It was raining that day. Was I suppose to go on my knees and do the rest of the inspection for them as well??? I was not involved in any accident. Visited the branch on Wednesday. Branch referred me to customer care. Contacted avis customer care on Wednesday to dispute their claim. Contacted them last night and this morning. No response received! Just the charge against my credit card