I purchased contact lenses with a voucher, got avios as a reward, spent those avios with others and after that got an email that
Unfortunately, shop has informed us your purchase no longer qualifies for the XxX avios originally added to your account, so they’ll be taken from your balance in the next 72 hours. We’re sorry for any disappointment.

But my avios account was zero (except for household) and after 72h it is still zero, no more.updates.

Will the deduct them later when it will be positive or I can assume that they cannot make my avios balance negative?