Hi @mariua2013, thanks for posting back to us, and sorry this changeover has not worked out well for you.
The first thing you need to do is contact Talk Talk to get your account with them closed. Once you've got this part sorted come back to us and we'll be happy to help you by reviewing the period you've been double charged.
That's ridiculous. Surely the customer is not expected to know or understand those sort of intricacies. A change of provider is a change of provider regardless of the technology and internal processes involved and should be consistent.
No denying it's complex, when the OP mentioned what happened, the only thing I thought of was 2 different technologies or a 2nd line was installed, not many second lines these days and FTTP is available to more properties.
It's not consistant because the switching process is designed for a working line takeover/transfer, this is more akin to switching to VM, the copper line remains unaffected as the broadband is FTTP and the voice element if taken will be DV, this will become more common in the next few years, along with other issues that will happen.
Industry processes will have to adapt to keep pace with new technologies.