Vodafone minimum speed guaranteed dispute

sotnale

Hi everyone,
I joined Vodafone's superfast 2 broadband in January and all was fine until the lockdown happened. I kept getting disconnected very frequently and got in contact with Vodafone over facebook (which is one of their preferred contact methods). The speeds kept dropping lower and lower due to the disconnects until it was below the minimum guaranteed of 55 mbps (this is the "sync speed" to the router which is shown on their app they have). They said they'd look into. The net was more stable at those speeds, dropping out 2-3 times a day but I could live with that. 
Almost a month has past and under their terms, if after 28 days the problem isn't fixed, I could leave fee free. At this point, the speeds are about 30mbps, half of what I'm paying. So I contacted them to see if anything is being done...and suddenly, my speeds increased to 60mbps, a little over the minimum! This is was just before 28 days (I think 26). The disconnects have now come back and are very frequent, happening every 15 minutes or so. The speeds are decreasing as before, but they have dropped to 55mbps, the minimum guaranteed and aren't dropping any lower unlike before.
I am in contact with them again to see what they can do but they are fairly useless suggesting it's my wifi and doing the same steps as before. It seems rather suspicious that they increased my speeds just above the minimum and seem to have locked it there so that I can't leave fee free.

How should I proceed? I obviously can't accuse them of this as I have little proof and it could be a coincidence.  If bumping up the speed is their "fix", then it was fairly useless given that the original complaint is the disconnects.