Free sandbox for testing in Azure

I'm really struggling here - I've created a free azure account for experimentation and teaching myself the basics and have built an application within it to add a login with Microsoft feature to our cloud computing software which works well. I need to allow other organisations to access the app if they are to login with it as I will need organisation logins for using a lot of the graph api stuff like sending emails. I think I should be entitled to a free sandbox account and if I login to VS subscription it gives me the option to add but because I have already built the app in Azure before I registered for VS subscription, it won't let me use it. Any ideas? I can only create one azure account as I only have one phone number and I don't think I would be able to transfer teh app I have already built to another account. I don't seem to be able to contact Microsoft anywhere about this without a support subscriptions which is weird because they surely want all of our mutual customers to login with microsoft and use all their Microsoft office products in new and more efficient ways.