Emmissions

Hello Im Jock an old disabled grunter, who at moment is stranded ,"Car less",I live 5 mile from nearest town,i attend hospital weekly but now cant so thats how important my car is,took it for MOT on 18th feb, failed on various minor things, couldnt find a garage to do repairs all busy or just not interested impression given by one so called mechanic,anyway 23rd Feb took to garage in town by AA relay, after spending threehundred pound, missing the date to return for first MOT they had to fail another one,so now its 11th march and they tell me they couldnt get emissions low and it needs a new cat converter, so i agree to pay another two fifty that was put on and guess what now Im told still wont lower enough,, so now I have a peugeot 309 and a £550 bill and still no MOT..they suggest its an engine problem with backpressure and can put sealant in cylinders to fix problem.as you will understand im at wits end and savings all gone and still stranded.
Looking for suggestions what do I do now