Failure to pay out claim amount that was agreed on

I submitted a claim for an accident on my vehicle. The claim was approved, after much back and forth, but on condition that I use the repair centre of the insurers choice. I did not agree to this as I wanted a repair centre of my choice. After much argument and back and forth the insurer agreed to allow me to repair my vehicle at a repair centre of my choice. An indemnity letter was sent to me to be signed which detailed the claim amount less the excess that the insurer would deduct. I was satisfied with the amount and signed the indemnity form. I subsequently received payment in my account which is R 3788.17 less than the amount which was agreed upon. I contacted the call centre and they cannot give me an answer as to why the amount differs. Since day 1 I have had issues with this claim. I pay my insurance on time and do not expect this kind of service.Ininformed the insurance that the vehicle in question is used for business purposes and as a result of the claim not being handled timeously, my business has suffered. The consultants do not know what is going on and the managers fail to follow up with the client. Not satisfied at all.