What to do if my landlord did not honor an agreement to refund my security deposit?

Landlord-tenant relationships are governed by state law.  If, under the law of your state, the landlord is wrongfully retaining all or a portion of your deposit, then most state laws have a penalty provision allowing the tenant to recover 2 or 3 times the amount of the deposit, plus court costs, plus ATTORNEY's FEES if the tenant has to resort to suing.  The "American Rule" is that (while the losing party pays the court costs) each party is responsible for the payment of their own attorney.  There are limited exceptions to this "American Rule" and, in most states, one exception is the award of attorney's fees to a tenant compelled to sue to recover their deposit.  This is called "fee-shifting."  Many tenants' rights attorneys are willing to take deposit refund cases on a "fee-shifting" basis so that you can have the legal services you need at no cost to you.  The deposit refund process frequently starts by your sending the landlord a written demand for a refund (date, sign, keep it short, provide a forwarding address, keep a copy).  Again, consult with a tenant's rights attorney in your state.