How to control your suppliers in such a condition

In such a company,how to control your suppliers.

A company has about 100 suppliers.

The company is a small company. Three years ago it was built. Then it began to source some suppliers. The suppliers began sending samples. And some suppliers made some moudles for the parts.

Three years later, the suppliers have made a big progress in their businesses. But the company is still small.Even the purchase order  which was promised in the beginning is not completed.Some parts are not purchased after the samples are approved. Of course the moules fees should be paid.

My question is how to control these supplier quality.