The tie pair was originally a term for your connection from the main distribution frame to the other licensed operators equipment (the end of your pair of wires from your house in the exchange, to a room, also in the exchange, housing LLU equipment). It is now, however, a generic term for any connection to any DSL equipment in the exchange.
It's use as an excuse for lack of service seems to be common, with many folk happy to believe an SP that the 'tie-pair' issue is 'BT's' fault, when in truth it may well be a lack of spares on the CP's own equipment, or the SP stalling the punter whilst they await the arrival/completion of having their own kit installed. Another favourite, when lack of sync has been proved to the SP's kit, and they have been informed, is them just doing nowt about it.....
When all is said and done, I doubt that you are bothered where and with whom the fault lies, you just want it fixed. In this matter, you only have one course of action. Your chosen ISP, in this case Orange, is whose customer you are, and it is them you must pressure for a solution.