Billing Troubles

I have been talking to the PT and SLP billing people this week. This is the first that I've heard from them about my bills for services since we've been in CDSA since last June. We have been asking for bills for some time and didn't want to get surprised. They are now telling me that the amounts that I understood that I have to pay are incorrect, and that I have to pay more.

My understanding was this: The provider would send the bill to insurance first, my insurance would pay and then I would have a copay. Then, based on my sliding scale, CDSA would pay a % of that copay and I would pay my %. In 2010, my copay was $25 and my sliding scale was 40%, so my understanding was that I would be responsible for $10 per session. In 2011, we upgraded our insurance to the more expensive plan (specifically because of these therapies) and our copay is now $20, so my understanding was that my copay for this year would be $8 per session.

The therapy groups say this is incorrect, and I am being charged $19.55 per SLP visit and $15 something for PT (I haven't seen the PT bill yet). They are telling me that they bill to insurance first, then when the BCBS payment comes in they bill the *remainder* to CDSA (not the BCBS copay, but the total amount minus the BCBS payment), and then CDSA determines their allowable and pays their % and I pay my %.

The actual breakdown of charges/payments on my SLP bill (for a 2010 session) are:
Charge from provider $100
BCBS payment $19.37
CDSA payment $29.33
Family owes $19.55
Write off $31.75

My interpretations are:
Total BCBS allowable $44.47
Total CDSA allowable $48.88 (I owe 40% of this)
Total collected by provider $68.25

My questions:

1) What is the actual way that my share is computed, and why is it different from what I thought? This was apparently not adequately explained to me in the beginning.

2) How can the provider collect more than the BCBS contracted allowable rate after billing through insurance? BCBS pays them based on the allowable charges, and I would think they are not allowed to try to collect the balance (besides the copay) after filing it through insurance. It seems to me that by billing BCBS, they are agreeing to the BCBS allowable amount, yet somehow through this arrangement they are able to collect 1.5 times the BCBS allowable amount. If I was not working with CDSA, they would not be able to collect more than the allowable rate from me. If my CDSA sliding scale rate was 60% instead of 40%, would I be asked to pay $29, instead of the lower BCBS copay? That makes no sense.

3) What is the CDSA allowable based on? Is it affected at all by how much my insurance pays? Will my amount owed per session actually change at all for 2011 due to my change in insurance level? BCBS is paying an additional $5 to the provider now (lowering my "copay" from $25 from $20), but will this just end up being another $5 for the provider? Will it just decrease my actual payment by $2 (40%)?

4) If I was not going through insurance at all, what would my payment be through CDSA? If I have to pay $20 for the session, and my BCBS copay would be $20 anyway, what is the benefit of my going through both CDSA and insurance? I might as well just go through my insurance alone and pay the $20, or go through CDSA alone. In that case, I wouldn't have to worry about whether the providers are on my insurance or not (such as the CLC therapists), or about running out of visits with my insurance.

5) Why must it take so long to discover how much I actually owe? We have been with CDSA for 9 months, and I am just now starting to see bills and discovering that my bill is double what I expected this whole time.