I'd guess that your EVSE (wall box) is 3-phase with a 20 A limit. So it would be able to charge at 14.4 kW if a car could use that power, but on a single phase (as the MG and many other cars especially in the UK use), only a third of that is available, or about 4.8 kW (depending on the exact mains voltage, and how accurately the EVSE and car on-board charger specify and read the current limit). The Mercedes EQA only charges at 11 kW because that's the car's on-board charger limit.
So unfortunately, there isn't much you can do about that. I guess you could install a second charger for the MG with a 32 A limit, but that might not be feasible, depending on the details of your house wiring and electrical supply. 4.8 kW isn't too bad for home charging. The MG will charge at 7.4 kW at 95% of public AC chargers (there would be a few 11 kW chargers, which will result in only 3.6 kW into the MG).
Some European MGs come with an 11 kW 3-phase on-board charger, so it might be possible to have your MG's on-board charger and associated ECUs upgraded, but it would be a quite expensive job, and not many dealers or third party operators would have the skills to do it.
