Bitcoin has change in November or December and a tx is kept in mempool 2 weeks instead of the old 3 days. But...
If you, a friend or simply the wallet re-broadcasts the tx from time to time, it can stay much longer.
The fee is very low compared to the standards of 1/1/2018, but in the last 2-3 days the spam on the network decreased a lot and the low fee transactions like yours may have a chance.
So, you should wait more. Keep an eye on
https://btc.com/stats/unconfirmed-tx to see the mempool is still decreasing. Use
https://pool.viabtc.com/tools/txaccelerator/ at every hour :00 sharp until your transaction is accepted. These are the easy free solutions.
If you want to pay, ask for help from the ones accelerating transactions for a fee, but you should pay after the acceleration or use escrow, since some are scammers.
There are ways to re-send the tx with higher fee, but they may be a bit complicated.