I used Hushed, have done for a number of years. Call and text from a virtual number, and it's all through the app. You can turn off notifications too to keep it even more discreet
It's around £3 for a 7 day number that comes with 20 minutes of call, or the equivalent in texts (60 texts)
Or you can get a 30 day number for around £6 that comes with 50 minutes calling time, or the equivalent in texts (150 texts).