Do I Have to Do Everything That's Asked of Me at Work

I've been in my current position (marketing) for over 9 years now. I like the job and the people I work with. Lately, though, my boss has started asking me to do things that, in my opinion, I don't have the time for, the skillset for, nor the pay rate for. Example: I was hired for my graphic design experience to create marketing pieces, design logos, and maintain a couple of WordPress websites. These responsibilities keep me busy for 40+ hours a week.

A couple of years ago we hired an independent company to get our social media presence established. They have a team of six working on everything from SEO to Google/Bing advertising to posting on four popular social media platforms. My boss is now asking me to "hold them accountable" and make sure everything they're doing is the best it can be. I've never done any of this before and feel like it would require lengthy training (I've been looking into it). In order to properly hold them accountable, I feel as though I'd need to know more than they do.

Another example is with the websites. I know my way around WordPress, but I don't know how to code in CSS (or anything else for that matter). He's now asking me for fancy behaviors that would require a skilled, experienced coder.

When I tell him I can't do "X" his response is always the same: "Take a class," or "Figure it out." Honestly, if I learned everything he wants me to know and did everything he wants me to do, I'd be working 80 hour weeks. There's a reason companies have TEAMS and DEPARTMENTS; because one person can't do it all. If I had those skills I certainly wouldn't keep working here for the salary I'm making, but I don't want to leave and have to start all over again somewhere new.

I know they want me to do all this new stuff because they want to stop paying the company we hired, but I've already been told there's no money in the budget for raises and asking for one could send me to the front of the line if/when layoffs ever come up. I haven't had a raise in 9 years but I have survived two rounds of layoffs.

I know the answer is to find another job, but I really like what I (currently) do and it's close to home. The salary isn't great but it pays my bills. I've also had more than my fair share of atrocious jobs and don't want to land in another that's potentially worse than this. Oh, and I'm 54 so finding another position wouldn't be that easy.

Is it unreasonable to tell my boss I don't want to be a graphic designer AND a coder AND an SEO specialist AND on social media? Honestly I don't see how asking that of someone could be anything but a recipe for disaster.

Advice, please!