[Other] WHAT??? RCN Charges for using their wifi in the 3-in-1??

I have a T-6 with 3-in-1 modem/router since November. Two days ago my wifi disappeared. I re-booted the router and all is good. Today I received a letter in the mail from RCN, advising me that they "inadvertently enabled" the wifi function on the 3-in-1 even though their records indicate that I "have not opted to subscribe to the wifi service", and that they will allow me to continue to use it until the end of the year free of charge. WHAT??? Is this April fools day or something?? Since when do they charge to use the wifi on the router? Isn't it enough that I pay for the router itself? What does it even COST them to have the wifi enabled? Can someone explain to me what's going on? Thanks.