I own a 2000 toyot mr2 spyder with 115,000 miles. I had an oil change went 100

What is your question?

After 100 miles no oil. The garage told me I needed a new oil plug, another oil change....about 30 miles no oil. Brought it back to them and they said it was burning the oil.!!! How can a car go 30 miles and burn that much oil? They said it was not leaking and my muffler had black soot which they said means it is burning it. What do you suggest?