Thanks for posting your question here, betsyp.
While the option for us to contact your customers and it's impossible to reach out to them and pay their invoices, you might want to record and consider it as bad debt. When invoices you send in QuickBooks become uncollectible, you need to record them as a bad debt and write them off.
To start, you can create a bad debt expense account. Here's how:
Afterwhich, create a bad debt item which we'll use in creating a credit memo.
Then, create a credit memo and link it to your invoices. For more details about the process you can use this reference: Write off bad debt in QuickBooks Online.
Keep me posted if you have other questions. Feel free to post them here.