My first post...apologies if too long and detailed and hopefully posted in the correct place! Opinions on Marriott stance would be gratefully accepted.

I'm currently having a prolonged battle with Marriott over the correct allocation of points for a stay in London in early December. I prepaid 2 rooms, having accessed their website via shops away, which would also earn me Virgin miles.
There were problems with billing at checkout but they were resolved.
My next issue was that I saw a spurious deduction, with no details of date or property, of 45,000 reward points for a reward stay. Turns out it was for one night of my pre-paid cash rate for this stay. Also, a lack of points were credited for my stay - base points woefully deficient and no elite welcome gift. I flagged this with the rewards call centre and the 45,000 points were re-credited and they would request copy bills for the hotel to correct the points.
I then noticed that my 2 miles transactions with shops away had been disqualified.
I emailed my missing miles query to shops away and contacted the hotel directly. I was put through to a front desk manager/supervisor. She was very helpful if totally lacking knowledge in shops away and the intricacies of Marriott reward scheme. She tried to explain I couldn't have miles and points but I got her to agree to go and investigate after I explained both to her. She didn't help things by setting my expectation of exchange rate applied being way in excess of the actual exchange rate when converting £'s to $'s. She was then going on leave so her colleague (front desk manager) picked this up and sent quite frankly an insulting response with a total lack of understanding of the situation and the programs. I asked for escalation and received a further email
My reward points had been increased and reflected the elite welcome bonus but were still incorrect in my opinion.
In the meantime I had correspondence with shops away who explained that Marriott had amended the transaction value on one booking and disqualified the other as the last click of the transaction was "not recorded as through shops away, but another source."
I challenged both and was advised they had remove VAT from the one transaction - fair enough but why apply it in the first place! The other, larger one was still void for the same reason they previously gave, namely that it was made via another source. I have challenged this as it was made via shops away and I'm surmising the issue is down to the double dipping of payment they made with the debiting of reward points from me.
My escalation resulted in receiving an email from the font office manager.
He admitted procedural errors with the incorrect deduction of reward points and advised he would seek to sort out the points and miles.
I replied and sent all correspondence and reiterate all details of my spend to enable this to be sorted.
He replied last night and is still attempting to engage with the correct people in respect of shops away but is insisting the reward points earned are correct.
This is where I cannot confirm if his answer is correct, which was basically ex-vat spend of £821.06 for rooms and food and beverage spend and this has been converted to $1,013.7, as Marriott use a pre-set conversion rate which does differ from the market rate.
I replied late last night that they have used an exchange rate of $1.23 per £, which was 18.6% below the prevailing market rate of $1.511 per £1 on 6th December.
I await responses from him on both the exchange rate and shops away and from my further challenge to shops away.
I also mentioned compensation over the hassle and time in attempting to sort this and have finally got their offer of 15,000 points - I haven't accepted or rejected this yet.

Thoughts on the exchange rate, shops away stance and compensation offer would be appreciated.

Thanks in advance.