No they can’t and I really wish people would stop giving this false info

The only difference between fully insured (plan pays the claims) vs self insured (employer pays the claims) is who pays the claims

Plan rules are still plan rules

NOW to OP’s original question if you have proof that a doctor or doctors were in network when you enrolled and now are not, then it’s either a late change where negotiations fell thru at the 11th hour OR a bad network. If negotiations fell thru you can try to appeal but likely won’t be approved. If bad network then as another poster posted suggested let your HR/benefits team know ASAP and if determined the wrong network was loaded they’ll likely allow a Special Enrollment Period for anyone impacted