An Instagram account is only required if you intend to sync your catalog to Instagram. If you’re just looking to sync your products to Facebook, you don’t need an Instagram account.
Could you please confirm if you’re being forced to link an Instagram account? `
Please provide us with a screenshot so that we can see what you are describing.
When setting up the Facebook connection on the second step of that process did you deactivate the Instagram Shopping setting which would be this one below?
Deactivating that particular setting during the configuration process did not force me to choose an account for Instagram and I could then complete Facebook the connection process on my test installation.
When testing I used the latest version of Facebook for WooCommerce which is v2.3.1.