Gear stucks in reverse gear ( gear phasta hay )

In my corolla 2005, I got it new zero meter ,from 1st day till now ( now mielage is around 31,000 km) its gear has some problem.
Gear stucks in REVERSE gear only,(gear reverse lagane mey phasta hay) it shows friction while getting in REVERSE gear,It never gets REVERSE in 1st attempt, always we have to tried it & put in REVERSE gear in 3rd or 4th attempt,when u want to put reverse it doesnot go smoothly it stucks & cause some "grig-grig" sound (like 2 iron rods are striking). IT GOES VERY SMOOTHLY IN REST ALL GEARS FROM 1,2,3,4,5 ; ONLY PROBLEM IS IN REVERSE.

i checked it more than five times.

one time when mielage was under 1500 km, at that time the mechanic said it is usual,nothing to worry, it happens sometimes,after 5,000-6,000 it will set automatically

when it was at 5,000km I again took it for checking , at that time mechanic told me that alhough this is new car but still gear oil is little low so he put very little quantity of gear oil in it .& he said me that drive sometimes, after sometimes this problem will solve itself after it, I drove it but not so much difference occurs but only sometimes little difference that noise gets decrease (very little) but gear still stucks

when I took it at above 10,000 with same problem, they again said that may be your driver doesnot press excellator fully ,that's why it get stuck otherwise nothing to worry ( although it was wrong because from 1st day zero meter me,my friends,family,driver all are using it & all are complaining of same problem), I told them I checked it from 1st day & myself ,they said gear is fine
i then left this as it is because sometimes gear goes in 1st attempt

when I took after 15,000 km, this time they said may be some wear tear in your gearbox so get your gear oil little drain out, they flushout some old oil & put 1 litre new gear oil.but problem remains same

when I took after 20,000 km, this time they said may be there is some dirt in gear box or some wear tear or may be some small air or water enters in your gearbox so get your gearoil fully changed, they flushout all old oil & put new gear oil.
but problem remains same
again i then left this as it is because sometimes gear goes in 1st attempt while sometimes you have to try 2-3-4 times

when I took after 25,000 km, this time they said no problem it happens in some car ,do one thing when your car gear stucks in REVERS put it in 1st gear,move your car little & then stop & again put it in REVERSE .( in some car this problem comes that it doesnot get reverse direct) but it is not serious
this time this technique works sometimes but not all time but main problem of stucking remains same

at 30,000 km,this time mechanic said that clutch plate is problem, when gearbox was opened ,he told that pressure plate is fine, only cluth plate has to be change,so he changed it & again put new oil but no diffrence at all

now same problem when I want to take reverse gear, it goes in 1st attempt only 5% while in rest 95 % of time it goes in reverse in 2nd,3rd or even 4th attempt while it goes smooth in 1st- 5th gear

anyone having similar experience or any idea about problem , So please tell me what could be the problem & solution?