We have used our allocated quota of 100Mb.

Also told that we have used our allocated quota of 100Mb - surprising

I did check your account and found that you have exceeded the allowed submission limit of free plan. In free account you can receive up to 100 submission but you have already received 110 submissions. That is the reason why your account is over quota and your forms are disabled. 

To activate and enable your form again, you will have to upgrade your account or wait for the first day of next month when the submission limits are reset.