Hi melanie
Just to be clear, the company has contacted you through facebook without you ever disclosing your facebook details to the company, and you strongly suspect that the company obtained your facebook details through your former friend (also a former employee of the company). You would like to know whether the company's conduct amounts to a breach of your privacy, and any remedies you may have
Why is the company contacting you? For supposed unpaid sums? Or in order to advertise goods and services directly to you? Or another reason? These details can be quite relevant, so it'd be really useful if you can fill them in before we respond in depth
Here is a recent Lawanswers thread in response to a similar question (goo.gl/RXzMGv) about a person's friend providing that person's personal details to a third party. You might find it useful as a starting point
Of course feel welcome to ask any further queries you may have
Hugh