Very bad internet connection

I've been suffering with this bad internet for a week. I can't get my work done. It's an expensive offer but I only got the first months to be working well. The rest it has been going down hill.I paid for 3 months at first then I went to pay and they told me that my internet has been limited and it will be fixed after payment. But after I paid, things got even worse. I went to your support on site and they told me to wait. Then they told me to call the "Service Technique" I did and the guy told to shutdown my modem for 3 minutes. I'm getting so annoyed with this and I need it to get fixed.