Seeking Confidence levels on returned samples

Hello all

I've run a survey, asking organisations to returned a number of surveys based on the size of the population they work with. I've based this sample size for each organisation on a margin of error of 10% and confidence level of 95% using the following formula

Sample Size = (Distribution of 50%) / ((Margin of Error% / Confidence Level Score)Squared)
True Sample = (Sample Size X Population) / (Sample Size + Population – 1)

Now that all my data is back in I can see that a number of organisations did not return sufficient numbers of surveys. There is no opportunity to go back and seek more surveys.
I now need to figure out what confidence level I can give to a number of returns, assuming that the margin of error stays at 10%.

For instance.
One organisation was asked to return 67 surveys based on a population of 221. They returned only 19 surveys. Keeping the margin of error at 10%, how would I calculate the confidence level.

I'm guessing that I can re-arrange my formula but I'm currently drawing a blank on to how this would work and whether it would be viable to do this.

Any ideas?