The 6 months free offer is only for those that are not subscribed or who have not had a subscription for the previous 12 months. Since you said you have been subscribed for quite a while, you would not be eligible.
This offer is for new and qualified returning subscribers only. If you are not currently a subscriber to Apple Music, and you have not previously subscribed to Apple Music or Apple One within the last 12 months or had access to Apple Music through a Family Plan within the last 12 months, you are eligible for this offer.
https://offers.applemusic.apple/en-ph/six-month-music-offer
The 3 month free trial with phone purchase is for new subscribers. If you have never had a subscription to Apple Music, you would get 3 months for free with a device purchase and would need to accept the offer on your device. If you do not see that offer, then you are not eligible.
New subscribers only. $10.99/month after trial. Offer is available for new Apple Music subscribers with a new eligible device for a limited time only. Offer redemption for eligible audio devices requires connecting or pairing to an Apple device running the latest iOS or iPadOS. Offer redemption for Apple Watch requires connecting or pairing to an iPhone running the latest iOS. Offer good for three months after eligible device activation. Only one offer per Apple ID, regardless of the number of eligible devices you purchase. Plan automatically renews until cancelled. Restrictions and other terms apply.
https://offers.applemusic.apple/new-device-offer
