they "went out of business" and our new auditing company requires bioburden testing.
this company is very bad in working with us to make the process easier.
I'm assuming you are referring to Notified Bodies. Your previous NB probably didn't "go out of business" per se, but rather either its notification was withdrawn because it wasn't up to the required standard, or it got out of this business voluntarily because it realised it can't keep up with the required standard and stay profitable at the same time. There have been known cases where "easy going" NBs went "out of business" in this manner, in the last few years, as the Competent Authorities have been trying to raise the bar (and not without some reasons).
Your current NB is not "making the process easier" - perhaps they're simply doing their job, as originally meant to be. Given the current trend, I'm not sure you will easily find another NB that will be "very good at making the process easier" for you.
The MDD ER 8.1 says:
The devices and manufacturing processes must be designed in such a way as to eliminate or reduce as far as possible the risk of infection to the patient, user and third parties.
(Manufacturing processes include in process monitoring and controls)
There are no specific bioburden testing requirements, but unless you can confidently establish that you can "eliminate or reduce as far as possible the risk of infection to the patient" without sterilization and bioburden testing, I think the NB's requirement is not out of place.
My question is, we're setting up bioburden testing and how can we know if "the rules are going to change" next week? ie, frequency of testing etc. Bioburden testing is not cheap and we need to know the rules to plan for the future, too simple, right?
The rules won't "change next week" because there are no hard and fast rules spelled out in the regulations. It is your job to establish and rationalise your testing regime. Bioburden testing is about control over your production environment and process and about stability. I would recommend testing every batch for the first 3 to 6 months (depends on how many batches you make during that period), then start to relax (every other batch, once a month, once every 3 months etc.) based on good results and a stable trend. Thereafter you need to monitor bioburden at a frequency deemed sufficient to alert you if anything starts to deteriorate (eg 1, 2, 4 times a year, depending on the specifics).
Don't forget that bioburden is not only about the numbers of CFU found, but also about their types.
You may further consult EN ISO 11737.