There seem to be a number of factors which need to be sorted.
First, why have you lost your NCB ? This should only have been cancelled by your insurance company if you had made a claim against them. Surely you have not done this ? All claims in this case, if your facts are correct, should be...
...girls as young as 11 years? I must have missed the bit where they repealed the law which said that sex under the age of 16 is illegal. Can anyone tell me when under-age sex became legal?
Sounds as if you have a "fixed-wheel" bike, with only one cog and no gears. Is this right?
If so, you'll have to change the cog, and possibly the whole rear wheel.