If something goes wrong on a job, first try to resolve it in the job thread — most issues are a miscommunication and a quick message sorts them out. Keeping the conversation in-thread also means there's a clear record.
If you can't resolve it between yourselves, contact support (see the Contact section of the Help Center). Our team can look at the job, the messages, and the invoice to help reach a fair outcome.
For anything involving your immediate safety, contact your local emergency services first.