Best answer by Transparent
Firstly, it can take around 4 weeks to arrange the transfer date. Once OVO apply to the national register to take over your meter, there are still several checks that have to be made. It is responsibility of the receiving Supplier to verify the details of address and Meter Number, not the Supplier relinquishing your account.
Secondly, I believe there is a six-week period at the end of a Contract, during which your existing Supplier may not levy any Exit-charges. That's why you tend to get calls/emails from Comparison-site companies at that stage. Perhaps an OVO Moderator could confirm this?
Thirdly, don't worry too much about getting exactly the right changeover date. I've changed Supplier many times, and I usually do a Meter Reading about 3 or 4 days in advance of the agreed contract-change date. I have never been charged for these final few days by the old Supplier.
The reason I take the readings a few days early is to ensure that all parties have an opportunity to query the readings if they think it's markedly different from their estimate.
If your reading is within a few percent of what's expected, it isn't worth the time and money for the original company to insist it is verified.
Hope that helps.