It have more than 12 wordpress websites. But for each website, I have had to make a new purchase. I know there is some feature called wordpress multisite network. But I am unable to activate it on any of my purchases. I am using managed wordpress services.
I would like to know if there is any way to make this feature open up so that I can manage my websites from single login other than JetPack?
With respect, if you haven't gone to the trouble of Googling the subject of multi site yet, I get the feeling you expect a simple solution that someone else will provide to you. That simple solution doesn't exist as the multisite network is not something easy. Like you have to be serious enough to really sit down and learn all of the basics first before you work with it. Otherwise your life will be much simpler just to work directly with your 15 sites.
Here is a tutorial of how to load the multi-site network. It may give you a good idea of how detailed and complicated it can be. Like you have to really go deep into it and spend time with it, in order to be able to use it efficiently:
I have a feeling too that you may find it difficult to install it on a free shared hosting account where you are going to need a wild card domain ability. It's better to do this on your own VPS where you have a dedicated IP.
It is easy.
[1st]First you have to create your subdomains, or an * WildCard subdomain(not sure about this one).
[2nd]Secondly you have to modify your wp-config.php file.
1 /* Multisite */
2 define('WP_ALLOW_MULTISITE', true);
[3rd]Third step: Login to wp dashboard, Tools > Network
[4th]Fourth step: Follow the steps indicated by WordPress and add the lines it says, in it's corresponding file(wp-config.php or .htaccess).
[5th]Fifth step: You should be able to use the new feature.
If not, check out a better guide.
You can do that by trying out a search on Google with this keywords : "how to enable multisite wp" and you will find some well written articles on the first page.