National insurance giant UnitedHealthcare plans to cut up to 700 Massachusetts doctors from its physician network for seniors enrolled in its private Medicare plan as a way to control costs, according to company officials. For elderly patients enrolled in the plan, the cuts mean they will have to find a new doctor or eventually switch to a new health plan that covers their current doctor. The move, effective Sept. 1, follows similar cuts made by the insurer to its Medicare Advantage provider networks in 11 other states... There is also pending legislation in Congress to prevent health plans from cutting...