(1) No insurer shall refuse to renew a policy unless such insurer or its agent shall mail or deliver to the named insured, at the address shown in the policy, at least twenty days' advance notice of its intention not to renew. This section shall not apply: (a) If the insurer has manifested its willingness to renew; nor (b) in case of nonpayment of premium, except that notwithstanding the failure of an insurer to comply with this section, the policy shall terminate on the effective date of any other insurance policy with respect to any automobile designated in both policies.
(2) For purposes of sections 44-514 to 44-521:
(a) An insurer's substitution of insurance upon renewal which results in substantially equivalent coverage shall not be considered a refusal to renew a policy; and
(b) The transfer of a policyholder between insurers within the same insurance group shall be considered a refusal to renew a policy only if the transfer results in policy coverage or rates substantially less favorable to the insured.
(3) Renewal of a policy shall not constitute a waiver or estoppel with respect to grounds for cancellation that existed before the effective date of such renewal.