We buy cars

My wife just bought a bmw 800 gs. From We Buy Cars It was a A rating motorcycle which mean ( will go through road worthy and can be financed)front shock are leaking. Back brake light are not working... today I have notes the engine number does not correspond with the invoice from We Buy Cars. ....what if it is a ****** engine...what must I do.... can't believe a big JSE company' sells you a motorcycle which the paperwork does not match. Scary ..