About the billing: still no discount after switching to KPN

Dear Sir/Madam,

I have had internet from KPN for more than 2 years, and this January, I was contacted by KPN that I could benefit by having also a mobile number from KPN. I was told that after having the mobile number I would receive some discount for the internet service.
I accepted this offer and I switched from T-mobile to KPN. However, it has already been a few months since obtaining the mobile phone number, the amount on the bills for the internet service still remains the same.

Could you please let me know whom I can contact?

I look forward to your kind help.

Best,

--

Liangliang