Woodstove chimney danger - help please

Hello to any experienced woodstove chimney people.... We have got ourselves into a very difficult position by having taken bad advice and done all the wrong things with a woodstove. Any opinions & ideas much appreciated - we are very despondent at the moment. (We also have very little spare money!! I'm retired)
Last autumn we installed a largish box woodstove (Jotul 602N) in a masonry chimney (brick built in about 1935) having been told it was in good nick and we could put the stove straight into it through a baffle plate. We did. Because we needed constant background heat we burned the stove near tight shut all winter - the worst way, now we know, for creosote/tar build up. Made worse by a cold loft space the chimney went up thro.
Result, tar seeping out of the chimney pointing. We got new advice and were told we had no option but to brick the chimney up, never use it again, and install a separate insulated flue. Do we have any other safe options which will let use re-use our chimney? Any way of cleaning up effectively? Lining with insulated flexible liner - would that be safe in the circs?
Help please.....

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