Firstly you'll need different CVs depending on the job you are going for. So take the one saying "Did python for 5 years at XYZ corp" and change it to "Did python and C# for 5 years at XYZ corp" - This should get you past the HR gatekeepers and in the meantime you just have to skill up on c#. When you reach the interview with technical people they will be more reasonable - providing you are actually comfortable with c#.
On this point remember that "5 years C experience" != "5 years commercial C experience".
If you were doing commercial-grade programming in Uni (or before) or any open source then consider that valid experience.
Finally, just because a job says 5 years experience, and you don't have it, doesn't mean that they won't consider your resume if you submit it. Better to hear the hiring manager say "no" then not submit your resume at all. Case in point, I don't have a college degree but I think every job I've ever held in my 12 years in this industry has asked for one on the requirements. I don't have one but I can do the job so I just applied anyway otherwise I'd never work!
/\ Try bending the truth.
Firstly you'll need different CVs depending on the job you are going for. So take the one saying "Did python for 5 years at XYZ corp" and change it to "Did python and C# for 5 years at XYZ corp" - This should get you past the HR gatekeepers and in the meantime you just have to skill up on c#. When you reach the interview with technical people they will be more reasonable - providing you are actually comfortable with c#.