i need to sue a vendor!

september 2018 a check was cut . a prepayment to vendor to make a specific color cmu block in the amount of nine thousand units once the sample was accepted. over the course of a year after seven failed attempts they attempted to deliver 4400 units to site. they were rejected and sent back. the footing or foundation had been installed prior to delivery of block.because of delays the contract was terminated in the amount of $ 127,000 for that first phase and the second phase was terminated in the amount of $212,000.we lost over $ 35,000 for footing and the deposit has still not been returned, All toll we lost over $374,000 dollars in revenue because of this.we have requested funds be returned for over a year but now iam ready to sue for full amount of contract lost? how do i proceed. the responses and communication on their end has ceased. the y just will not make this right and now im over it. please help david murphree/ owner/ operator masterkraft masonry