unblock iPhone 7

I have an iPhone 7 which is out of contract with the phone provider.

I have changed phone provider and want to use the phone but it is locked

I called the phone provider and they said they have no record of the IMEI and thus won't unblock it

The phone was definitely purchased through them and I have a record of the date and contract but they are unwilling to help in any way, they are being incredibly unhelpful

In this instance is there any way Apple was unblock the phone for me? I can provide the contract detail, date of purchase etc

many thanks