College Reference Question

So my background investigator contacted me early last week and needs the contact info for one of my professors that I had during college to conduct an interview with them about me. I was told they needed this info by this coming Wednesday. I've tried emailing 2 of my professors who I knew the best and I know would remember me, but it's been 5 days and I've not heard back from either one of them. I've sent them both follow up emails 2 days ago and still heard nothing. I don't think any of my other professors would remember me if I emailed them. If I don't hear from them by Wednesday, what should I tell me investigator?