I suspect that they might be yellow jackets rather than bees. Yellow jackets are smaller than bees, and can be quite aggressive when defending their nest. Have you seen lots of these insects at this nest site? They can best be observed during the day. Try to make a positive ID of these insects before making another attempt at spraying.

Here is a link that might be useful: {{gwi:1004385}}

A quicker, less expensive way to be rid of the yellow jackets is to wait until dark and pour hot soapy water down the hole. If a few make it out, they won't be able to see you to sting you.