P and O are the only carrier currently conveying Foot Passengers between Calais and Dover, and then only on 3 sailings a day- late morning, mid afternoon and early evening.
There is a previous thread about ethical concerns over the Company and the condition of their ships.
Also the port has now relocated and is a long way from Calais Ville station, furthermore there is now a 90 minute foot pax check in.
The reality is that this is a barely viable routeing now, only for the very determined with a whole day to spare.
No coach picks up in Calais or sets down in Dover. You have to go from Paris to London then backtrack to Dover if that is your final destination. Check the timetable very carefully for each coach as most use the car Shuttle in the tunnel. A few use one of the other ferry companies- DFDS or Irish Ferries. Again this is a long journey, but the only way to do it if you are set on using the traditional ferry route, and /or if cost is the key driver.
It is far faster and overall more convenient to use the Eurostar train from Paris or Lille Europe to London St Pancras, and forget about Calais entirely. Eurostar is not calling at Calais Frethun until at least spring 2024, and don't bank on it happening even then.