Attorney-General is the way to go, IMO. Keep track of statute of limitations. With their legal staff, there is no excuse for documentation. Keep a paper trial. If you are close to tolling of the statute of limitations, see a lawyer. The gifts were gifts. Loans are different. Perhaps they feel that she is alive and don't feel that you have the capacity to receive the documentation without a power of attorney or some written consent.
Also, write to the Executive Director. They must have a corporate address separate from their general address. Speak with legal.
The A-G's Office will write them a letter, notifying them that you filed a complaint. I cannot overemphasize how a letter from a state agency moved work at a large law firm. It was a hot potato. Matters that lingered for months and years had to be resolved within 24 hours. I write over small consumer matters. A-Gs must be very effective. Many times I only have to threaten. One item from my own experience -- low level customer support may not know enough to even care. They can ridicule you. If you call the main corporate office, a different type of customer service rep is there. They have the power to make deals. Legal action, reporting to an agency scares them.
Are you certain that your mom may have forgiven the loan? She may not have realized the implications. You need to establish concrete facts as much as possible. Would she forgive such a large sum without consulting you or a lawyer? The WT may simply be too lazy. The A-G should make them run.
Regardless of legal position, with all the money she gave to them freely over a long period of time, they could provide documentation, treat you cordially, and do some work.