You cant really call the garage and 'go crazy' as your car was in there over 6 months ago, and I assume that when they had fixed the fault you were happy, until recently when it has gone wrong again.
The sensible thing would be to have the fault diagnosed by an independant company and IF the fault is the same as before and the part they replaced is faulty then you can return with the report and inform them that the part is faulty and enquire about the warranty that the part comes with, most genuine parts will have a minimum of a 12 month warranty. They will then claim for a replacement part and fit it, however there may be some labour costs depending on the parts/labour warranty that the garage offers.
Most part manufacturers have a claim system that the garage can use to claim lost labour time caused by parts that have failed within warranty, ask them.
But in short, you cant blame the garage that installed the part 6 months on. Its probably the fault of the part, or more likley a completely different fault!