Visa On Arrival extension

Hi,

I'm from The United kingdom and would like to know if I can get a visa on arrival from you.

I came to Vietnam on my original visa in May 2017 and have extended  my visa 4 times since then.  I tried to extend a further time but was  told I cannot get any more extensions.  I'll exit Vietnam to either  Cambodia or Thailand next week and hope I can get another visa back to Vietnam if possible.  

With this is in mind, would it be a problem for me to get a new visa on arrival with you?
 Thanks