Try to call paypal and explain the situation , if they don't believe and they leave the Chargeback as it is then there is two options :
You probably don't even know much about PayPal; using it to buy bitcoins is against their terms of service. AFAIK, the buyer had every right to chargeback (even though it's a selfish and stupid thing to do).
[1][1]And sorry, but that is in essence what you are risking every time you sell bitcoins for PayPal. Although this is probably too late, always trade with a trusted partner.
1. Make a new fresh Paypal account. (I would do that)
2. Deposit the required money on the current Paypal account and get your balance back to normal . (I wouldn't do that If I were you).
I doubt he would willingly throw away a PayPal account he has been taking care of for 6 years.
*Edited because I mixed up the sides.

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