I didn't read your question carefully, just saw your mapping took you out of the insert mode and the last <esc>
... my fault.
You want to map ctrl+;
vim cannot capture the keycode. there are some key combination cannot be mapped in vim. ;
is one of them, another example like ctrl+=
.
so you may want to choose another mapping.
btw, you can try in insert mode press ctrl-v
then the keycombination to see if it could be used.