seems odd that they would agree to something they don't do, why not just say no.
Culture, and money. In those places where VM locate their first line customer contact centres people see it as culturally unacceptable to offer a response of "I don't know" or "I'm working off a script, I don't know what you're talking about and my script doesn't cover the thing you want me to help with". The money side is that those contact centres are not just offshore, they're outsourced to other companies, and those other companies want to meet certain measures such as average call handling time, number of calls resolved first time (and many other measures), so by fobbing you off with a blatant lie, you put the phone down happily, they chalk up another call as resolved and quickly.
If an agent had offered that and you'd taken account of that when agreeing a contract with VM, then even as a verbal promise it becomes legally binding and enforceable. But under all other circumstances there's no reason for VM to pay, no legal requirement to pay, and I'll wager there's no form to complete or process to follow.
Important edit: You say you were told this before the connection was made and before the 14 day cooling off rights ended? If so there might be hope, as you had the option of cancelling the VM order at that time without penalty under your consumer rights. If you took the information about VM paying the other ISPs ETC into account as part of the decision to continue with the contract, then it becomes binding on VM. That's because The Consumer Rights Act 2015 Section 50 part 1b covers that - you'd agreed a contract with VM, but after you'd agreed it you took into account information provided by the company, at a time when you had options other than remaining in contract. If this applies and you wish to assert that it does, then you should know VM will not comply easily. You will need to make a formal complaint to VM, that complaint will be rejected, fobbed off or ignored, and you'll then need to take the matter to Ombudsman Services. All depends on how much is at stake, I would guess.
But I still say it's not company policy, there's no process, no ETC claim form.
