Complaint Review: merchant's

Last week I asked to check what was wrong in my car due engine alert light was on. They told me I had to change tune-up. I reminded them I already changed tune-up last year. But they did not listen and changed tune-up. But engine light was still on. They said no idea what happened and asked me go to other auto services to repair.  I was surprised and asked them refund due nothing fixed. One manager shrugged. Yesterday I went there to ask re-checking my car because we felt something getting  worse inside my car and I believed that they would find the reason it happened easier. One manager asked me to come next day because of only one worker working there.  This morning I came to this services again and the same manager asked me wait until 11 am. I awaited for three hours and half. Many guests came to get serviced before me. 11 AM finally came, one manager surprised me and he still asked me went home or go to other dealer's without re-checking my car. I felt not right and felt helpless because i am deaf. They thought i was easier to copy with or fool.

How can you help me to solve it?

Lin