
A Great Giveaway!
Received and activated my hosting account. Thank you very much, AbeloHost.
PHP code got broken, Emails got closed "automatically" after the "advanced upgrade"... can't send (not checked extensively though)/receive emails. I haven't tested what else has been damaged on my site.

There are other addon domains which I haven't modified since their upgrade, and they are still working without problems. Only the 2 sites, this main site and a subdomain which were slightly modified, that too after changing the theme (not even added,modified, or deleted any WP plugin), causing all the php codes working through a good plugin simply vanished leaving only the header and footer visible! Thinking that the theme was the problem, I reverted back to the default twentythirteen/fourteen themes, but the site's php codes aren't working any more... I even tried replacing the said php plugin (which helps execute the php code in WP pages), but nothing is bringing back my site to normalcy now.
The content, wherever it was populated through php and database have vanished! The pages where there is textual content, e.g. on Contact Us / ToS, etc are not affected. Even email service is broken... I have a few global variables declared on this main site, which were working fine before, but may be that has been the cause may be because the security has been tightened too much at the backend. That's the only reason I see, but then why should the site's email service get affected?
The above problems are only for the said domain and its subdomains which were modified after the backend upgrade was done by the host.
There are two other addon domains, but I don't use them so much, and there is one WP+woocommerce site which is working fine till now. I don't know if it will break too if I add another plugin or do any php etc (coding) modifications there.