Best answer by Transparent
The Energy Ombudsman has made it clear that it is the responsibility of the Receiving Company to initiate all processes of the switch.
If you already had a Smart Meter, then I'm guessing this problem wouldn't have occurred because DCC would be able to verify identical readings being sent to both Suppliers!
Although it is common practice for the Original Supplier to request that you take a manual meter reading on the agreed switch-date, as I understand it, it is the Receiving Supplier who should upload the Meter Reading to the National Database. The Original Supplier then gets a notification that the reading is there and has the opportunity to challenge it... for which there is a special process.
In your case it would appear that the Original Supplier is holding out that their reading is correct. Frankly this isn't your problem!
As the receiving supplier is OVO, you should email firstname.lastname@example.org, restate the meter reading you took on the switch date, and request that this is sorted with the National Database.
It is most unusual for you to receive a Final Bill when there is still a dispute. The Final Bill should be generated a fortnight after the switch has correctly occurred (with the meter reading agreed). That's because the customer still has 14 days cooling-off period under the terms of the Consumer Credit Act.
The reason for the Switch-process working as I've described is that it must be able to operate if a Customer has fallen out with the Original Supplier. The Receiving Supplier initiates everything so that you do not have to communicate any further with the Company you are leaving.