Dissatisfaction with dealership

On 29th September I took my car into the dealership to check a noise. On inspection the mechanic and service manager checked that the vehicle had no lubricant. Bare in mind they acknowledged that the oil light was not reflecting on the dash. I left my vehicle for repairs only to receive a call two weeks later informing me that warranty is not responsible due to lack of lubricant and based on the false report that the light was on on arrival at the dealership they refused to pay.Yes , there was no lubricant but why didn't my oil light come on. Bare in mind I have three other vehicles and I'm an experienced driver surely, I won't overlook an oil light. Finally I have repaired the vehicle at my cost but totally dissatisfied wit the dealership and owner because they failed to answer my question as to why the oil light didn't come on. Also, for stating lies in their report that the light was on. I don't understand what they covering up because they refuse to do an investigation as to why the light didn't come on. This is not an honest dealership, my guess is they didn't replace oil at the last service undertaken by them.