Applicable law (see bolded portions) found here:
http://www.gencourt.state.nh.us/rsa/.../540-a-mrg.htm
Section 540-A:7
540-A:7 Return of Security Deposit. –
I. Except as provided in RSA 540-A:6, IV(c),
a landlord shall return a security deposit to a tenant and pay the interest due, if any, within 30 days from the termination of the tenancy. If there are any damages to the premises, excluding reasonable wear and tear, the landlord may deduct the costs of repair from the security deposit. The landlord shall provide the tenant with a written, itemized list of any damages for which the landlord claims the tenant is liable, which shall indicate with particularity the nature of any repair necessary to correct any damage and satisfactory evidence that repair necessary to correct these damages has been or will be completed. Satisfactory evidence may include, but not be limited to, receipts for purchased repair materials and labor estimates, bills or invoices indicating the actual or estimated cost thereof.
II. If the tenant is required under the lease agreement to pay all or part of any increase in real estate taxes levied against the property and becoming due and payable during the term of the lease, or if there is unpaid rent due, the landlord may deduct such share of real estate taxes or unpaid rent from the amount of the security deposit. The landlord shall provide the tenant with a written, itemized list of any claim for unpaid rent or share of real estate taxes for which the landlord claims the tenant is liable, which shall indicate with particularity the period for which the claim is being made.
Source. 1985, 100:6. 1988, 167:2, eff. June 25, 1988.
Section 540-A:8
540-A:8 Remedies. –
I. (a) Any landlord who does not comply with RSA 540-A:6, I, II or III shall be deemed to have violated RSA 358-A:2.
(b)
Any landlord who does not comply with RSA 540-A:6, IV or RSA 540-A:7 shall be liable to the tenant in damages in an amount equal to twice the sum of the amount of the security deposit plus any interest due under this subdivision, less any payments made and any charges owing for damages, unpaid rent, or share of real estate taxes as specified in RSA 540-A:7.
II. Notwithstanding RSA 540-A:6, 540-A:7, and 540-A:8, I, a landlord shall not be liable nor forfeit any rights if his failure to comply with said sections and paragraph is due to the failure of the tenant to notify the landlord of his new address upon termination of the tenancy. Any deposits plus interest due on the deposit that remain unclaimed after 6 months from the termination of the tenancy shall become the property of the landlord, free and clear of any claim of the tenant, absent fraud.
III. Any provision in any lease or rental agreement by which the tenant is purported to waive any of his rights under this subdivision, except as provided in RSA 540-A:6, III(d), shall be void.
Sounds to me like the landlord owes you double. I would send them a certified letter with a copy of the statutes and say that you will expect to receive a check as outlined within 5 days. If you don't get the check, they be prepared to take them to small claims court.