You don't decline.
You raise your concerns with your manager, as your manager (and not you as an individual) determines the scope of your work and required access to systems and not the development team. If your manager says that you should be doing these things or having access to these systems and tools, then you work with the development and operations teams to get the appropriate training and access to do the work that is in-scope for you. If your manager says that this work is out-of-scope for your job, he should bring this to the attention of the development team and their manager.
If, after taking to your manager, you still feel that your manager's expectations of the work that you do and your expectations of the work that you do don't align, you can choose to resign your position and find a new job that is more in line with what you expect.
To follow up with the edit to the question.
If it has already been decided that it is not your responsibility, you should be informing your manager that the development team is (still) making these requests. Your manager should be the one to ensure that your time and effort is put on doing the work that is assigned to you. This is their battle to fight, not yours.
However, as a developer myself, I would (and would expect my manager) to push back on the idea that this is beyond your job. I find it suspicious (and unsafe) that the entire development team would have access to production systems and data. Since it sounds like your job is to do front-line support, I would expect that these people have at least read-access to system configuration and data and can include it in the problem report so it is much faster for me to reproduce and design a solution.
It still sounds like this is a problem that needs to be hashed out with management to make sure that everyone understands everyone else's role. It sounds like the company isn't that big, so it shouldn't be too hard for everyone.
To follow up once again with some of your comments, it sounds like your company's process has serious issues.
If you are submitted tickets to the Technical Support team, I wouldn't expect that the Development Team is involved at all. Maybe the Technical Support team may need some information from you, but I would expect that the Technical Support team would either fix the issue or pass it off the the Development Team if their assistance was needed. I would expect that the Development Team interfaces with the Tech Support team and not you for understanding the issues, only bringing you in if necessary.
Again, my original points still stand: Don't get involved yourself. Talk to your manager and have him work with the managers