I have a Samsung TV with Freeview, a few more channels than you.
Most TVs today are able to store 999 channels, ie 3 digits, so if you press just two digits it waits to see if there is a 3rd, even if you only have channels from 1 to 99
Try this, for any of the channels from 1 to 70, (or whatever the last one is before 100), press 0 first, then the number
eg for channel 51, press 051
See if that works.
I'm using an LG 26LS3500 TV which is not connected to a cable box, but does have basic cable input, ie, about 70-something channels.
When the first number of a two-digit channel number is entered, a drop-down box appears listing all the channel numbers that begin with that number (Similar Channel List). After the second number is entered, there's a five-second delay before the channel appears.
Moving channel to channel using the up/down buttons works normally.
Is this a customary "feature"?
Does anyone know how to disable it?