Which smart device solution to choose?

Question

Arduino

In short, I have a device for cosmetology, I produce these devices myself in China (Stuffing inside from Dwin). I sell and rent to clients.
Now there is a need to add a “blocking” module to block the device for those customers who do not pay rent.
We decided to do this:
once a month, the “device” blocks the device if the user does not enter the code.
After talking with experts, I see several solutions:

• Do it on Raspberry Pi/Arduino (add a GSM module) so that there is a full connection to the network, and then my specialist logs in via SSH and enters the password once a month if the client has paid.
  
• Just add a GSM module: and manage the device via SMS (as far as I know, MTS has a Mayak tariff that allows you to buy an unlimited number of SIM cards for 1 passport)
  

One of the experts suggested the option “do everything from 0”:

• Develop an FPGA board
  
• Add Bluetooth to device
  
• Next, make applications for Android / iOS and control the device from the application via Bluetooth. (After the device is locked, the user simply enters the application, enters the “password” and activates the device via Bluetooth for another 1 month)
  

If anyone has experience, I will be grateful for the feedback, the comments of experts in this field in the comments are very interesting.
Thank you.

Answer 1

On an arduino or ESP, we make a pinger that goes to the site via rest-api every month or when the device is turned on and asks for permission to start, if permission is received, it sends a signal further.
This on the Internet in simple training examples should be full

Answer 2

The simplest is a conventional controlled relay with GSM, which cuts the power inside the device by SMS command. Doesn't pay - sent a command, everything turned off. If it pays, then you don't have to turn it off. You can get around it by turning on the GSM jammer in the room, but if it has come to this, it’s easier to disassemble and connect the two wires bypassing the relay, i.e. this is not a defense against an understanding person. For example, relays are:
https://ru.aliexpress.com/item/RTU5024-GSM/3284966...
​​https://ru.aliexpress.com/item/RCmall-2-SMS-GSM/32...
https: //ru.aliexpress.com/item/RCmall-1-SMS-GSM/32...
Plus, you don't have to do anything: neither make a board, nor write firmware, nor make an application for your phone. FPGA is generally overengineering, it is not clear why.