Have you actually rung them and explained what they've done?
Sounds like its time to write to them, with pictures of the unacceptable work, so your complaint is traceable, and tell them you've lost all faith and will send the barrel to another supplier to be repaired. You will then send them the bill for the repair, and the total cost of your time and parts to date.
Tell them you've copied the letter to your trading standards (or US equivalent) and expect an answer within 14 days. If you don't get a satisfactory answer, you will expect a cheque within a further 14 days or will take legal action to recover your costs.
You've been reasonable enough!
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