Shiv from Sherwood Park

I got synthetic granite countertops in the kitchen and 3 bathrooms, in Dec 2011-Jan2012. I recently discovered long (1 - 2 ft) cracks in the countertops in two bathrooms. I contacted the vendor with a photograph of one crack. Their response was an offer to fill up the crack. My query as to likely causes of cracking, how durable the fill-up would be and request to consider more concrete measure (rather than superficial remedy such as filling the cracks) has remained unanswered. As well, the quality of plumbing was sub-standard. I still have evidence of this. My call about plumbing issues earlier was not answered at all.