Buyer requested bank chargeback 7 months after accepting an invoice

I completed a project with a buyer at the end of December 2019. The buyer has now, 7 months later, and after being happy with the project and willingly accepting it, has requested (through his bank) his money back via a chargeback. Has anyone had this experience before? I have money in my escrow that I cannot withdraw, I am worried that PPH will take all of my money from the escrow that I have earnt through completing other work, to pay for this chargeback. Bearing in mind I have 4.9 stars and 16 completed jobs.

It's obvious that this buyer cannot be trusted, why would someone accept the invoice in the first place if they wasnt happy? Anyone had a similar experience?