If you want to enter the competitions here are some things you can do to make it difficult for them to contact you afterwards.
From a previous post of mine about the DNCR
"If you provide your phone number on a web site or when you enter a competition, to register for example, then you have given that company and any linked companies with whom they share data permission to disregard the DNC register, they always put this sharing clause in their privacy policies. So if the site owner or competition holder shares this info with their advertisers and so on you basically wipe your DNC request. This is why many people put themselves on the list and then a little time after start getting flooded with calls again.
If you want to try to stop this and have a mobile phone you can buy a prepaid SIM card for a cheap service that has a 365 or 180 day credit expiry period examples would be ALDIMobile $15 +$5 (SIM cost) 365 day expiry, Amaysim $10 + $unknown for SIM 365 day expiry, Vodaphone $10 + $unknown for the SIM 365 day expiry. Register it and use that phone number anytime a site asks for one. It may cost you about $20 but the peace and quiet may be worth it. If your mobile phone is locked to a service then ALDIMobile uses Telstra, Amaysim uses Optus, and Vodaphone uses Vodaphone 
Just swap the SIM card out once you have your new number and place it someplace safe just in case you need it for some contact over an order or similar, so it can be used for a few calls when you want, and to put a recharge on it before the expiry date (to keep the number active). Put a reminder in your Calendar for a few days before the expiry date so you can ensure you refresh your SIM credit. A bonus is that if you do pay and activate the next recharge before the expiry date most rollover the unused credit.
I hope that helps some of you to reduce or eliminate these calls."
Then to the email question I recommend using disposable addresses. Some email providers give you some but there are companies/businesses/sites that offer unlimited disposable addresses. See this article for some:
I use Blur from Abine (basic version which is free) but as can be seen from the article above there are more. I prefer Blur as my masked email addresses are permanent unless I turn them off. Blur has some other free tools I take advantage of and these are a tracker blocker, and a password generator/storage component. You can visit their site to read up on it here:
https://www.abine.com/index.html
I hope you find the hints useful.
