Greetings.
I'm an Italian freelancer, working from years on the SEO field. I've already worked for similar projects (check ***https://www.freelancer.com/u/valentinafurno.html?ref_project_id=4958305 - Ferga ***) and I know quite well how to handle situations like this.
First of all, I SEARCH all the backlinks pointing to your website (they may be thousands). Then, I SELECT the toxing ones, using pro tools developed only for this purpose. In the next step, I send an email request for these links to be removed. Please, understand that it's not possible to force someone to remove a backlink, pointing to your website, from "his" website, that's why I repeat this step (asking for the links to be removed) three times.
During this process, I keep trace of this work with a gmail account created for you. If nothing changes in the 45 days, I write a disavow request to google, proving the work done to remove the toxic links.
Usually, google removes the penalty in a reasonable timeframe. The last time I fixed a website hit by Panda, google took 3 months to remove the penalization.
This is not a fast job and if someone tries to sell you faster results, you're being cheated. Also, I'm not selling you backlinks, nor I've no interest in selling you a monthly plane or whatsoever. What I want is, for you, to revert from this situation.
Please, keep in mind that this is my standard, basic offer. I could edit it according with the number of backlinks pointing to your website.