Manual port forwarding IS the way to go! Once done properly it should be fine.

Yes I had similar problems late last year & earlier this year with service going down for same reasons. Upgrading of exchanges & lines between here & the main service point. A total PITA. I was forced to use dial up over that time. Did they tell you that you can use dial up over those times? And I 'think' I was offered a discount at one point in time due to excessive loss over a week or so. I can't remember.