Did you try this
php bin/magento module:enable Vendor_Extension
Although giving it more thought it might have disabled itself due to invalid key. Does have any kind of activation key?
If in doubt I would contact the extension developer.
while the code migration script is available:
but I think that for the sake of your business you should buy the same extensions for Magento 2.
Development and maintenance costs will be even much more. Count yourself - proper working shop is more important, ...