Hi
You may not have a filter actually fitted in the relevant space, unless you have air conditioning.
If it's not accessed through the top of the dash, try removing the plastic trim at the base of the windscreen on the outside. This is held with a number of torx head screws into plastic bushes.
If you have no airflow, it's unlikely the filter is completely blocked. Can you hear the fan turning, and is it fast enough ? If not, you need to first check the electrical feed by measuring the voltage across the two fan motor terminals on all the speed settings. On full whack the fan gets 12 volts, on lower settings it is reduced by a variety of resistors. The speed switch and resistors are in the earth return side of the fan motor. If the resistor pack is faulty (it has a thermal fuse inside) you may only get the full speed setting (resistors bypassed).
If the voltages are OK, check for a siezed or partially siezed fan, for example one of its plain bearings may have gone dry and tight or there may be something jamming it.
I attach a corrected Fan schematic for the X244 model posted in the past - Thanks to Communicator or whoever posted it originally. If you have aircon there are differences.