How Can Spasticity In The Neck Be Treated?

I had a stroke eleven years ago and I still am unable to walk. My right side is Ataxic, but not spastic. There is a a lot of spasticity in my neck however. After my stroke and before I had Botox injections in my neck, my chin (and my head) was always in my chest due to the spasticity of the muscles in my neck. It hurt to lift my head due to the spasticity in my neck. After nine months I got Botox injections in my neck. They definitely helped me. I could lift my head for the first time since my stroke. I have gotten Botox injections every since (the Botox is only effective for three months). Last year however, I went a span of five months before I got Botox injections in my neck (due to a change in doctors). Ever since then, I still get Botox injections in my neck but they don t seem to be as effective. My head is starting to slide back in my chin, due to the spasticity in my neck. I do neck stretching exercises every day in between Botox injections. My doctor has increased the dosage of Botox when he injects my neck, but nothing seems to work. My head is starting to slide back into my chest. Either I went too long between Botox injections or my body has built up a tolerance to the Botox, or both. Has anybody under gone a treatment that is effective against spasticity other than Botox injections?