Can I pay for more than one year at a time?

yes, you can (but be aware that the first year is a discounted rate, and thereafter will increase).

contact adobe support per @Nancy OShea 

p.s. if you're contacted by anyone (via email or private message), it's much more likely to be a scammer than an adobe representative. ie, double check for an employee badge if contacted in the forums and look for an adobe.com domain in the email address if you click reply to an email. then check again and be very suspicious. any other method of contacting (or offering to contact you) is almost certainly a scam.

p.p.s you can also use phone (but chat is usually quicker), https://helpx.adobe.com/contact/phone.html

[Moderator moved from Using the Community (forums) to Account, Payment & Plans.]

I don't think so.  I suggest you contact Adobe support and ask the agent about that.

CONTACT ADOBE SUPPORT:
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Online Chat: https://helpx.adobe.com/contact.html?rghtup=autoOpen
Phone M-F, during normal business hours: https://helpx.adobe.com/contact/phone.html