Obtaining a Schengen visa extension is difficult, see Is it possible to extend a tourist Schengen visa (12 more days)? You could still try to contact the consulate and ask if they would be willing to change their visa but they definitely don't have to do it.
Regarding your second question, apart from long-stay visas or residence permits (which are quite difficult to obtain as well), the only kind of visa that can be used to enter and stay in Spain are Schengen visas. In principle, you should always apply to the country that will be your main destination and all Schengen countries have to apply the same rules and follow the same procedures, so that none of them offer a quick online visa that would allow you to circumvent the Spanish consulate.
Your main options at this point are therefore the following:
- Complete your trip as originally planned, using your current bookings, and leave before the end of your current visa. It's probably frustrating but it would not cost you anything and would increase your credibility for future visa applications.
- Start a fresh application with the Spanish consulate, providing all the necessary documentation again. The consulate certainly has the power to extend/revoke and replace their own visa or issue a second one covering the rest of your stay but you will have to pay the fee again (and possibly quite a bit of money to change your bookings, with no guarantees that it will work) and they will reevaluate your application completely.