WeBuyCars: Broken Promises

I purchased a car in Sep 2023 from WeBuyCars Germiston, the car was handed over just for them to suddenly realize that the road worthy certificate had expired. When I took the car for the inspection it failed, which WeBuyCars repaired. No problem. One of the items was the battery that was replaced. WeBuyCars provided me with Invoices for all items replaced/repaired. Needless to say; the car started giving problems and after getting stuck several times and many trips to a mechanic it was identified that the battery that was replaced at WeBuyCars was already 4 years old. A supposed new battery dated 2019 was placed into the car in 2023. Fortunately the guarantee is valid from date of purchased 2023. We buy cars promptly assisted in getting the battery replaced. Now the problem I have - I have been struggling for around 4 weeks to get an invoice for this new battery. I need this for the guarantee as I do not wish to have the same hassle as before. I have been made promises several times in writing that it will be sent. Each of these promises have been broken. I am not asking for much, just a simple Invoice. Can it really be that difficult to provide a customer with this document. I have been extremely patient and understanding. Not one person has come through. For the purpose of the complaint, I will provide names of these individuals should WeBuyCars contact me. As I would really not be nasty to the point of embarrassing them on a social platform. Please, I beg, I need to Invoice for the new battery placed into my car.