Help! They sent me notices of infringement of copyright of Shutterstock and Photos5

I received an email about 1 year ago from Shutterstock.com and another email from Photos5.com with a "Cease and desist claim and offer to resolve the claim of copyright infringement".

I have used some photos I found on Google and some desktop wallpaper websites on my business website, and these images are protected by copyright (which I did not know at the time, and I had the impression that all The images on Google are free, Shutterstock requested $ 273 and Photos5 offered me a $ 150 deal to resolve the copyright infringement within 10 days before taking legal action.

I ignored both emails and deleted the images immediately and never returned them, they sent me many emails during that time asking me to resolve the case before involving lawyers, but I ignored the emails because I already deleted the images from My websites, and their The last email was to inform me that, since I did not pay their settlement offer, they will sue me, and their images are copyrighted and registered in the copyright office, etc., and I did not hear from them. after that.
SEMrush

Two weeks ago I received an email from Shutterstock to tell me that they are going to handle my case to a contracted copyright enforcement organization, that I have also ignored their email.

BUT now I have received a registered mail letter from an Intellectual Property lawyer in my area representing photos5, and I have no idea how they found my address or my real name (my domain was protected by Whois) informing me that they have already started to be legal actions to recover legal damages, it seems, the copyright infringement involving images registered in the US Copyright Office. UU allows legal damages of up to $ 30,000, or $ 150,000, if it can be proven that it was a deliberate act. !!! It's just an image !!!

I contacted them and I offered to buy the image and pay the previous settlement fee of $ 150 and close the case and I am very sorry, but they replied "we are contractually bound not to talk to you", and should discuss this Only business with your lawyers !!

What should I do? Should I hire an intellectual property lawyer because it is too expensive, or should I negotiate directly with your attorney, do I need help please? Any advice is very appreciated.