Sheets2GCal is provided by GCalTools operating as a registered French Individual Enterprise (Gerstenberg: Siret: 534 063 912 000 16 not liable for VAT).
Contact Sheets2GCal: sheets2gcal at gcaltools.com
Contact GCalExtras: gcalextras at gcaltools.com
For bugs and other technical problems you can also post to Github at the links below:
Sheets2GCal:
GCalToolkit/Sheets2GCal/issues
GCalExtras:
GCalToolkit/GCalExtras/issues