Paypal is the 800 pound gorilla. EBay sellers are pretty well required to accept PP, and the other acceptable electronic payment services are about the same price and are looked at askance by buyers, so most sellers don't bother with them.
And most sellers are not able to qualify for a credit card merchant account which costs as much or more than Paypal. Our family business has over 35 years to build our reputation, and still many of our online customers prefer to use PP rather than make direct cc payments.
Sometimes when you run into a problem you just need to toss your cookies, turn off the computer, take the cat for a walk and let the glitch work itself out.
If that doesn't work, to the Paypal site and try their Resolution Centre. They may even have a North American call centre to help you. Write down the sequence of events before you call. It will clear your own mind and will help the clerk a lot.