I also have the aquafish and it does send an sms daily to the number mentioned. I am not too familiar to the Linux commands but have enabled developer mode and have executed the commands of stopping the service and masking the timer. The sequence followed by me is first I stopped and disabled the service as nemo with user option, then I stopped and masked the timer as root with and without user, then I again stopped and disabled the service. using journalctl I can see that is returns the value that the timer is stopped I am not aware how to check the process is disabled or not if somebody could guide me I would like to check it out Let me see what happens
systemctl --user status sms-activation-intex.service