It appears that your corrective actions are ineffective. Your C/A verification activities are your internal audit results, in this case, and they are telling you what you need to know. I would begin by scrutinizing your problem solving process.
Ensure that your problem solving activities result in positive corrective actions to address the specific root cause as well as recurrence prevention actions (there is a difference) to make the system more robust. Be sure to apply these actions to any similar products, processes, or systems that are at risk for experiencing the same failure.
Speaking of root cause(s), are you asking “why” enough times during your analysis? Maybe you are not digging deep enough and determining the “root” cause. “Root cause” is defined as “the lowest level cause that can be corrected”. Keep asking why until you can no longer come up with an answer. If that “cause” is something you have no control over, step back a level or two until you reach a level of “cause” that can be addressed with corrective actions.