justcloud.com didn't work, won't give full refund Internet

I paid $75 for a year subscription for their "cloud"/internet based file backup service. The software would only copy a small fraction of files before stopping.  I went through several iterations with their customer support, following their instructions carefully and providing clear report of problem. I am a senior level software engineer.  

It was clear to me that the service would not work for me. It took several further emails to secure a refund.  

I derived no benefit from use of the service, and originally requested refund within a week of subscribing. 

They refunded all but $15.   They refuse to pay the remaining $15, insisting on classifying this as "early termination", where it is actually "defective product".

I suspect that a significant portion of their revenues is unfairly derived from mis-application of this policy.