Where's the £1 gone?

A customer has got a £97.00 car repair bill but, being hard up this week, they borrow £50 from bank of mum and £50 from bank of dad.
 
Our customer then pays our bill and gets £3 change. Giving £1 back to mum and £1 back to dad, he keeps the other £1 himself.
 
So, now owing £49 to mum and £49 to dad, this adds up to £98, and adding on the £1 he kept himself, where's the other £1 gone?