The only ungrammatical part of the sentence is They are claiming that it was very low quality material that is why the hose became shrunk by heat … Here is my revision: It has been reported that the water vacuum hose of the floor-cleaning machine supplied was found to be shrunk by heat, supposedly as a result of the hose's low-quality material. Please ask the supplier to look into this matter and arrange for a genuine replacement immediately. I'm not sure if genuine is the right word here, but it's not my place to remove it.
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