Waiver of the subscription invoice after it has been generated

i have cancelled the zoom phone subscription but the billing invoice was generated and i don't have money to pay because of it the transaction has been declining.

I was about to cancel the subscription before hand but slipped from my mind and it got charged and it's been 10-15 days now.

I don't want to be a defaulter but need to clear the outstanding payment somehow.

Is there any way zoom could assist in this regard?