My Xbox Gamepass is overdue and so, suspended. Will it continue to rack up debt if it is...

No it won't rack up debt nut you will unable to cancel the subscription until you pay the outstanding balance.

It don't stack but you have to pay the open fee with a credit card or another payment method. Prepaid won't work on an open balance.

not stack of overdue but try to pay it if you can continue cancel it for a time and wen you can pay it again.

There isn't any need to worry. You may want to go online and stop auto-renewal/check what the renewal settings are on your subscription...once it gets authorized to be paid, it will then renew. In the meantime it'll just stay there and you won't be able
to use Gamepass until its paid.

No, but you won't be able to use it until the past due balance is paid.