Correct procedure to merge GMB pages for same business following relocation

[PeteKernow]

I'm waiting for GMB Support at Twitter to get back to me but wanted to check here first.
In February I relocated my office within the same city. Nothing else changed, same phone, email, website, and same services provided (I'm a therapist). Someone at GMB told me I couldn't change the business address on GMB, but would have to mark old page as permanently closed and create new page for new address. When I did this there was a massive drop in ranking and consequently less inquiries. Recently I discovered this was bad advice. Contacted the chat service at GMB, the person there didn't seem to understand my issue but advised to reopen the old page and he/she would then move or merge it. However I heard no more after reopening the old page. So I now have two GMB pages with slightly different business names, different locations in the same city, same email website and phone. Page A has much better ranking, page B has correct present location, both have some good reviews which I want to keep.
My priorities are to retain the ranking of page A and retain reviews from A and B, while showing only the correct address as on page B.
Should I ask them to MERGE A and B with the above specifications? Or should I ask them to mark A as MOVED to the location of B and transfer A's reviews to page B? Will I retain A's better ranking if I do this?

 

[JoyHawkins]

Does the new page have reviews yet? If not, I'd just delete it and update the old one.

 

[PeteKernow]

Yes it has some good reviews

 

[PeteKernow]

And I'm wondering also how long to wait for GMB to reply on Twitter, I replied to their first reply on Wednesday and heard nothing since.

 

[Rich Owings]

It's often two weeks.

 

[PeteKernow]

Thanks yes they phoned me after about two weeks, so I think it was the department where yuo book a phone-back that answered in the end. Twitter dept didn't get back to me and chat dept were clueless. They have now marked my old page as moved and say they'll merge reviews from the old page once I send them a photo of my signage.
This initially restored my new page to the good rankings of the old page. However now that I check again two weeks later my page has dropped right down and on some relevant search terms it doesn't even appear. It's extremely frustrating especially since I'm the longest established in my city in my profession and many of my competitors who are ahead of me have no reviews at all. Unfortunately Google has a near monopoly in this country (UK).