Generally speaking, if a claim on a life assurance policy is made and during a claim it transpires that the date of birth was wrong, the correct premium will be calculated and if you've been paying too little, any shortfall would be deducted from the claim. But cover is not invalidated by a genuine error on the date of birth.
My opinion would be that you were on cover on the original policy and therefore not entitled to a refund, although I'm not sure why your adviser didn't simply notify the life assurance company when the error came to light, rather than starting a new policy.