My toilet won't flush, and just adds water
Had a similar problem last year. Called a plumber and he found that the drainpipe was clogged by roots close to the street which prevented the water from escaping. If your toilet has an inspection outlet you could check to see if this is also full to find out where the blockage is. Next step would be to call your Water supplier to find out if the blockage is on their land (street-side). If they tell you the blockage is on your property, then you would call a plumber as they have the equipment to find and clear the blockage.