You are in year 3 of a 4 your course at university?
Arguably you should stick with it as much as you can as even if you did transfer you would have to redo quite a bit.
Also with languages, the year abroad and the regular contact would have a lot of advantage over just reading, listening and a much smaller amount of contact time.
If you did transfer to the OU it may be worth considering transferring to a slightly different degree, for example Business Studies with French, or European Studies.
You may, and I am not sure, be able to transfer what you have done in languages over so at least you don't need to redo much.
Distance learning is something I nearly always recommend people to consider. However with languages I am not sure if it is a good way of learning.
I am a natural 'distance learner' myself, but when learning languages I need the immediacy and 'forced' nature of classes and conversations for it to sink in.