There are two issues at stake: the correctness of the coding and the potential cost to your consortium in both time and money.
On the first issue, you could report the problem to Monitor, the independent regulator of foundation trusts, with a record of coding errors and the error rate because both the PCT and the trust have failed to act.
However, I suggest you alert the PCT and trust once more of your intention to go to Monitor if they fail to respond. I expect you will hear from them quickly.
On the issue of cost, I suspect that the reason the PCT is not engaging with you is that the errors are not inflating the tariff cost you pay. If this is the case and the error rate is low (10 per cent or less) you might think it best to let sleeping dogs lie, having raised the quality issue as above.
If it is costing your PBC cluster more, shout loudly as the PCT should be keen to sort this out. Also raise a formal challenge to the trust.
The real dilemma, however, is if the errors tend to be to your cluster's financial advantage. Morally you should still persist in asking for the coding problem to be addressed and acted on by the foundation trust.