I was denied workers compensation because of pre-existing injury, the company said that they do not pay for pre-existing injury.
what shall I do?

Was your pre-existing condition exacerbated by the new injury? You may want to appeal the denial. It is your right to do so. Workers compensation should cover at least part of the expenses if the new injury caused problems, even if it was complicated by the pre-existing condition unless your new injury was caused by gross negligence on your part, such as you lifting boxes were you were on a restriction prohibiting you to do so, etc.