Billing problems

I opted into the WindSource renewable energy program to pay an extra $0.01/kWhr for Wind energy with Xcel for multiple years. Last year, I wanted to try to cut back on spending and asked Xcel to opt out of it. They said that they would have it processed and removed from the bill a month or two later. A year later and with multiple calls and emails with Xcel, they still hadn't gotten it removed.

I filed a complain with the PUC commission. A few days or a week later, I received a call from the PUC and a second call from someone higher up in Xcel. Both of them apologized for the problem happened and assured me that it would be fixed and backdated to when I requested to opt out of the program, but it might take a while because of how understaffed they were. I was happy with this outcome and was willing to wait longer.
In July, a new statement came that refunded the charges ~$127, their math was slightly incorrect, but I wasn't going to raise a stink over a few dollars and was happy to accept it as resolved. Two days later, they added a second correction where they charged me an additional $281. So I ended up paying an extra $154 when I should have been refunded about $130.
I've had multiple calls with them since then, an additional PUC complaint, and assurances that it would get fixed from Xcel, but no one is fixing it. Today, I had a call where they suggested that the charges were correct. They're going to talk to their manager more about it and give me a call tomorrow. I hope that this resolves it, but I've had the same conversations with people at Xcel almost a dozen times and it hasn't been resolved yet.
I don't know what else to do when a company insists that their incorrect billing is correct and I can't get someone from the PUC to reach out. Do I do small claims court next? I don't know how to solve this problem and I just keep calling in every month when another statement arrives and the problem is still not fixed.