Alex Nash, from Cornwall, was invited to the party just before Christmas.
An invoice for 15.95 pounds was sent by his school friend's mother Julie Lawrence, who said Alex's non-attendance left her out of pocket and his parents had her details to tell her he was not going.
Alex's father Derek said he had been told he would be taken to the small claims court for refusing to pay.
However, they realised their son was double-booked and due to spend time with his grandparents, which he did.
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His parents said they had no contact information for Lawrence at that time.
They found the invoice in a brown envelope in his school bag last week.
"It was a proper invoice with full official details and even her bank details on it. I can understand that she's upset about losing money. The money isn't the issue, it's the way she went about trying to get the money from me," Nash was quoted as saying by BBC.
In a short statement, Lawrence said: "All details were on the party invite. They had every detail needed to contact me."
Nash said he had been told he was being taken to the small claims court because he was refusing to pay.