Will the wrong address on the v5 void the insurance or the write off payment? Thanks

I doubt it.

The policy address and therefore the risk/premium were presumably correct.

If the insurer tried to void the claim based on a genuine error from which no advantage accrued I think you'd have a strong case for the Ombudsman.

Time to argue IMHO. Insurers are meant to return you to your situation before the write-off, which normally means the cost of buying an 'identical' vehicle (give or take). You may have the option of keeping the car and having it repaired, but their payout will be less. £3K looks to me too little for either option.