I am afraid it is a very common problem among individuals suffering from CTEV (clubfoot), with not very successful treatment options.
People with Congenital tallipes equino Varus or clubfoot usually have surgery in the childhood, like you have, and that prevents severe leg deformity in the future.
Although the leg deformity is corrected a few residual flexing deformity usually persists and usually undergoes arthritic changes.
Although a few surgical procedures like arthosis are known to be done in adolescents with residual club foot, it is not very successful. I would not recommend it.
I would recommend the following.
1) Consider wearing special shoes for residual clubfoot, usually custom made based on the amount of club foot.
2) The main concern would be to reduce the arthritic changes in the foot and the first step towards that would be to reduce weight and have a regular exercise regimen.
3) Consider taking Aspirin 325 mg to reduce the pain and inflammation.
4) I would strongly recommend physiotherapy and it is the best treatment for your problem. It will increase the ability of the foot to flex and also help in improved mobility.
5) Strongly advise you to have a good healthy diet with good portions of milk and banana for Calcium and phosphorous.