How do competitors reach out to our online customers?

Question

CRM

Hello, I hope there are people here who can give a hint.

The situation is this:
We have a static landing page where customers can apply via a form. After filling out and submitting the form, the client goes to the "Thank you for your purchase" page, the data from the form is transmitted by a GET request , i.e. the url of this page looks something like site.ru/sale/index.php?name=test&phone=[phone] .
Further, the application falls into LP-CRM.

The most interesting thing is that after the client has sent an application, after a while our competitor calls him and offers the same product, but at a price lower than ours. As a result, we lose a lot of customers.
Changed passwords for hosting, checked the code of the main page and sale for extra scripts, etc., changed the password for CRM, but this does not help either.

People, tell me how they can implement this?

Answer 1

Alternatively, employees merge

Answer 2

say hello to the former developer and look for where he put the backing

Answer 3

Another option I can offer is this.
Mystery shopper.
You fill out an application yourself on your website, under a false name and phone number. Waiting to be called. First you ask everything, and then you ask a question on the forehead.
Where did you get my phone number from my site?
The option is so-so, but at least you can learn something.