If I saw double tick in Message module, does it mean that my contact has received & read my message?

If you see there are double tick, it is not necessary that all messages has been delivered or read. This function varies based on the channel you connect. If you connect to the below channel, please expect the following result

Channels	Available / Not Available
WhatsApp API - Gupshup	Available. Please enable it at your Gupshup portal (Gupshup dashboard → webbook → Message events settings)
WhatsApp API - Cloud API	Coming soon
WhatsApp Web	Coming soon
Facebook Messenger	Available by default
Instagram	Available by default. Only have Seen function.
LINE Business	Not available
Telegram	Not available