^As long as you're taking into account interest on the loan, which is included in the calculation of how much money you'd owe them total.
E.g. if your loan was $10,000 at 5% interest for 2 years and you made a $1,000 initial deposit against the loan, your interest would be ~$950 over those 2 years.
So the final math would be 10,000 - 1000 + 950 = $9,950 payable total, 50% of which would be $4975. So as long as you've paid at least that much, you can VT.
Curious, did you ask them about terminating early? Cause it's pretty dodgy of them to try and mislead you about what your cancellation rights are (if that's what they've done).