Question Summary:
Will the unpaid tax represent debt when I have tried my best to inform the authorities but they have failed to take my tax?

Question Detail:

I am a g.p (family doctor) working in the uk.  In 2010 i worked for 4 months as a doctor in australia, when i went over there, i found out that i would be self employed, IN OTHER woRDs I wouLd havE tO KeEP alL MY REcEIPTS/exPenses lisT AnD ThEN PAY tAx afTer.
I HAd TO lEaVe austrALiA In an emeRGency aftER 4 MONtHS BECAuse OF A deatH in ThE FaMily.
 AFTer coMING bAck To the uK, iN 2011 i SUbMitTed mY EXpEnSEs lISt TO My MANager iN AUStRalIa who FIlEd ouT an ETax form aND toLD mE tHAT HE SUbMItteD iT to thE taX oFFice in ausTRalIA. I Have hEARd NOTHiNG FROM thEM AND tHEN SeNt tHE TaX OFFice An emaIL earLIer ThIS Year and they sAid THAT THEy neVEr RECEIved mY etAx foRM. i Then emAIled my manager AND ASKed hiM TO ReSUbmit my ETAX foRm To thE TaX OFfIce SO ThAT ThEY cAN send me My tax BilL for ThAT 4 mONTh pERIoD, i think tHE TAX bill may be in tHE rEGioN of Up to £5000.
iN toTAl ovER thE LAsT 2 YEARS i HavE SENT MAYbe more thaN a dozen emAILS TO my mANAgeR thEre to chAsE It up so I knoW HOw mUCH TAX to paY. i JUst WANT To KNow THAT IF ANyThING WAS to happen To mE, IS ThIs AN UNpAID Debt that I wiLl bE Accountable for, IN THE SIGHT Of AllAH?
do i HAvE TO keeP on CARryINg on and try tO cleAR THis tax bILl oR CAN I JUST LEAVE IT NOW?
i JuST Keep ON GETTInG woRrIEd that it is the oNly 'debt' tHAT i havE. 
I suPpOSE thErE IS MOrE That i CAN DO, I COuLD RIng the australian tAX OffICE late AT NiGHT(ABOUt 11 HoUr time dIFfereNcE BETwEEN The uk anD AUstRalia) and ASK thEM what tO DO. 
thE EMail tHAT I received fRoM THE austRAliaN taX OFFIce SaiD THAT tHey haVe Not RECeiVEd mY eTAX FOrM AND TO RESUbMIt IT. I had iT sAvEd on mY dEskTOP SO i ATTacHed iT To an email and senT it to Them, tHey tHEn repliEd saying thAT tHEY COULD NoT oPen it uP, THATS WHEN I CONTacteD MY MANAGER AND ASKED HIM TO FORward it To THeM aNd HIs laST EMAIL SAiD That HE IS WOrkIng ON It.
 
pleasE TELL ME what I Should do, IF I DONt dO ANYthiNG anD THey nEver coNTACt me foR thE MoNEY- iSlaMiCally wIll i bE DoinG riGhT OR IS thIs AN unPaiD dEbT THat I hAVe To PaY?? 

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salaam ‘alaykum wa-rahmatullāhi wa-barakātuh.
You have tried your utmost best to contact the authorities and to return the tax money. You may ring the Australian tax office, inform them of your situation and make your money available for them to retrieve. If even after this, they fail to take any measure and retrieve the tax money, neither the money owed will be considered debt nor will you be liable by Allah[1]. However, in order to clear your conscious and practice on Taqwa (piety), you may apply your discretion and give an estimated amount due for tax to poor and needy persons[2].
And Allah Ta’āla Knows Best
Hanif Yusuf Patel
Student Darul Iftaa
UK
Checked and Approved by,
Mufti Ebrahim Desai.
www.daruliftaa.net