I couldn't trust my Pixie until she was over a year....I just think it takes these little dogs alot longer than other breeds...for whatever reason.
Just keep doing what you are doing...confining when not being watched, take outside after every meal, drink, playtime sleep etc...and reward reward reward!! EVERYTIME my Pixie goes out to potty she gets a treat from a box i have next to the door...she runs in and sits there waiting for it! even now she will still have the occasional accident...but its usually our fault for not reading the signs!
I'm pretty sure your little one will catch on soon...don't give up!