Astrid
Do not pay them. I have dealt with several of these companies on behalf of clients. In Australia they lock you into a 12 month contract. The fact is at law they have an obligation to provide a product fit for service - and they are not doing that. In fact from reading the blog only it seems they could be doing long term harm typical type operators.
Send them an email along the lines
"As you are appreciate various promises were made to increase site rankings using white hat practices.
Can you please detail exactly what you have done for the money paid to date. No further payments will be made and this contract ceases immediately if not done forthwith.
I have had several SEO experts review the website and the site now has a number of spammy bad links pointed at it. This is considered black hat practices and is rejected as a sub-standard practice by google webmaster.
I await for your response. If I do not get a detailed report within 7 days I will assume that the contract is repudiated.
I reserve my legal rights in relation to the damage occasioned to the business in relation to the spammy links"
Fight hard... these guys make our lives very hard..