Today faced with this situation, bought in 2016 addition - "WHMCS Notify Extended" especially convenient or useful to call it difficult, but how it worked. Last time we did not use this addition, it hung as a backup option.
Today, after a year and a half, the developer suddenly decided to bill for the update and support and immediately write off the money from the card. I did not see any updates from him even once.
After I wrote a question about the account and the money back, I just deleted the account and the license.
I wanted to know this only I was so lucky, or is it an action from the developer))
And what to do in such cases, how to find a normal product which, without such merry consequences?