Merge whatsapp accounts I have been using one WhatsApp number up until I went into another country where I started using a new number. 
In a new number I was joined into different groups and since WhatsApp allows one number per device I could not use old one. Now I want to merge my new number to my old WhatsApp account and have a single one. 

Is that possible? I contacted their support and they have not answered yet. 

I have both Sim cards in one phone
you can change the numbers by going into Settings>>Account>>Change Number.
Here you can Change Number form A to B and you wont loose your chats(data).
Also you can select an option if you want you contacts to get notification about this change.