my phone connected to my modem via the SPA112.
Whenever I call a place that has an automated message that says "press 1 for xxx, press 2 for yyy or press 3 for zzz" pushing the number does nothing it appears that the analogue phones signal does not get relayed correctly.
Your phone is connected to your VoIP provider via SPA112. Your modem, internet connection type and even phone model is not important for the purpose of issue you described. The "signals" in question are known as DTMF. You are true, DTMF needs to be relayed correctly from your phone to your VoIP operator. There are multiple ways how to relay them. SPA112 needs to be configured to the method supported by your VoIP operator. It's nothing we can guess or analyze - just configure whatever method yours VoIP operator recommends to you.
As a workaround/last resort solution, you ca use in-band type of relaying, but note the in-band is incompatible with compressed codecs, so use aLaw or uLaw (according your VoIP operator preference or according the native codec used in your country). This workaround may not work reliably, may not work to some destinations, or may not work at all. Correct relaying method based on VoIP operator advice is preferred solution.
