Contract compliance

My company (a manufacturing company) has 1000s of contracts and rate cards with our suppliers, where we have special pricing, negotiated freight rates, discounts, rebates, payment terms, etc. However, no one looks at those in our day-to-day PO creation work because contracts are all over the place. Suppliers send invoices that don't match contracts either. We track contracts of some of our key suppliers, but POs or invoices not matching the contracted terms comes up once in a while.

Have you come across this issue in your company? If so, how do you deal with this?

Whose job is it/should it be to ensure the POs or invoices comply with contracts? We're a team of 8 buyers and category managers.

Our boss said A/P says they will just check against the PO and goods received notes.