Oil change and suspension fix

I took my vehicle in to Tuffy for an oil change and some issues I was having with my suspension. After they had worked on it I began driving the vehicle normally again. I then began to hear an engine noise. I took it back to Tuffy they said I needed an engine replacement. I didn't believe what they said and took it to a Toyota dealership to have them look at the problem. I was told that the last place that changed my oil failed to refill my oil properly which led to me needing an engine replacement. We went back to the owner of Tuffy to get compensation and were laughed at and told to prove it was them who caused the damage. We have all the records and documentation proving this and were told good luck by the owner. I have contacted corporate Tuffy and I have not been treated as a priority.