If it is a business account that you have and you were dealing with the BT Business people you will need to post on the BT Business forum.
This is a BT Residential forum and can not deal with BT Business accounts.
Hi @Justamum and welcome.
I'm really sorry you've had such a terrible experience with BT. To be honest there isn't a lot we can advise on as this is the residential forum but reading through your post it looks like your residential account was cancelled during the takover process which would have resulted in held to term charges on any outstanding contracts and equipment.
You'll need to speak with the business team on 152 (I know you're in contact with them already)but when the new business line is connected I would think the held to term charges on the line which was ceased in error shoud be removed.