worst case scenario if charged interest use
http://www.thecalculatorsite.com/financ ... ulator.php
and click standard calculator and put in your total debt to start with and term 6 years and it gives you a summary, I put your21k in and 6 years and it returned this:
Year, Year Interest, Total Interest, Balance
1 £1,742.99 £1,742.99 £22,742.99
2 £1,887.66 £3,630.65 £24,630.65
3 £2,044.33 £5,674.98 £26,674.98
4 £2,214.01 £7,888.99 £28,888.99
5 £2,397.77 £10,286.76 £31,286.76
6 £2,596.79 £12,883.55 £33,883.55
the final figure is what the balance would be at the end of that year, so after 2 years 24,630 plus any fees, less any payments made.
though you may have signed up to a good firm that does as Michael said above, this is prob worst case scenario.